diff --git a/src/tiled/automappingmanager.cpp b/src/tiled/automappingmanager.cpp
index 9ddb6ff576..2b4e9bfc82 100644
--- a/src/tiled/automappingmanager.cpp
+++ b/src/tiled/automappingmanager.cpp
@@ -36,6 +36,8 @@
 
 using namespace Tiled;
 
+SessionOption<bool> AutomappingManager::automappingWhileDrawing { "automapping.whileDrawing", false };
+
 AutomappingManager::AutomappingManager(QObject *parent)
     : QObject(parent)
     , mMapDocument(nullptr)
@@ -85,7 +87,7 @@ void AutomappingManager::autoMapRegion(const QRegion &region)
 
 void AutomappingManager::onRegionEdited(const QRegion &where, Layer *touchedLayer)
 {
-    if (Preferences::automappingWhileDrawing)
+    if (automappingWhileDrawing)
         autoMapInternal(where, touchedLayer);
 }
 
diff --git a/src/tiled/automappingmanager.h b/src/tiled/automappingmanager.h
index 64e38385b8..146097a40c 100644
--- a/src/tiled/automappingmanager.h
+++ b/src/tiled/automappingmanager.h
@@ -20,6 +20,8 @@
 
 #pragma once
 
+#include "session.h"
+
 #include <QObject>
 #include <QRegion>
 #include <QString>
@@ -61,6 +63,8 @@ class AutomappingManager : public QObject
     void autoMap();
     void autoMapRegion(const QRegion &region);
 
+    static SessionOption<bool> automappingWhileDrawing;
+
 signals:
     /**
      * This signal is emitted after automapping was done and an error occurred.
diff --git a/src/tiled/documentmanager.cpp b/src/tiled/documentmanager.cpp
index 05c425c7ef..3750910db0 100644
--- a/src/tiled/documentmanager.cpp
+++ b/src/tiled/documentmanager.cpp
@@ -38,6 +38,7 @@
 #include "mapview.h"
 #include "noeditorwidget.h"
 #include "preferences.h"
+#include "session.h"
 #include "tabbar.h"
 #include "terrain.h"
 #include "tilesetdocument.h"
@@ -142,6 +143,9 @@ DocumentManager::DocumentManager(QObject *parent)
     connect(TilesetManager::instance(), &TilesetManager::tilesetImagesChanged,
             this, &DocumentManager::tilesetImagesChanged);
 
+    connect(Preferences::instance(), &Preferences::aboutToSwitchSession,
+            this, &DocumentManager::updateSession);
+
     OpenFile::activated = [this] (const OpenFile &open) {
         openFile(open.file);
     };
@@ -591,8 +595,6 @@ void DocumentManager::insertDocument(int index, const DocumentPtr &document)
     if (mBrokenLinksModel->hasBrokenLinks())
         mBrokenLinksWidget->show();
 
-    updateSession();
-
     emit documentOpened(documentPtr);
 }
 
@@ -891,8 +893,6 @@ void DocumentManager::closeDocumentAt(int index)
 
     if (!document->fileName().isEmpty())
         Preferences::instance()->addRecentFile(document->fileName());
-
-    updateSession();
 }
 
 /**
@@ -988,8 +988,6 @@ void DocumentManager::currentIndexChanged()
 
     mBrokenLinksModel->setDocument(document);
 
-    updateSession();
-
     emit currentDocumentChanged(document);
 }
 
@@ -1217,11 +1215,10 @@ void DocumentManager::updateSession() const
     }
 
     auto doc = currentDocument();
-    auto prefs = Preferences::instance();
 
-    prefs->session().openFiles = fileList;
-    prefs->session().activeFile = doc ? doc->fileName() : QString();
-    prefs->saveSession();
+    auto &session = Session::current();
+    session.setOpenFiles(fileList);
+    session.setActiveFile(doc ? doc->fileName() : QString());
 }
 
 MapDocument *DocumentManager::openMapFile(const QString &path)
diff --git a/src/tiled/main.cpp b/src/tiled/main.cpp
index dcf56dfafc..dbe8ba88bb 100644
--- a/src/tiled/main.cpp
+++ b/src/tiled/main.cpp
@@ -42,6 +42,8 @@
 #include <QJsonDocument>
 #include <QtPlugin>
 
+#include "qtcompat_p.h"
+
 #include <memory>
 
 #ifdef Q_OS_WIN
@@ -66,12 +68,12 @@ class CommandLineHandler : public CommandLineParser
 public:
     CommandLineHandler();
 
-    bool quit;
-    bool showedVersion;
-    bool disableOpenGL;
-    bool exportMap;
-    bool exportTileset;
-    bool newInstance;
+    bool quit = false;
+    bool showedVersion = false;
+    bool disableOpenGL = false;
+    bool exportMap = false;
+    bool exportTileset = false;
+    bool newInstance = false;
     Preferences::ExportOptions exportOptions;
 
 private:
@@ -185,12 +187,6 @@ inline T *findExportFormat(const QString *filter,
 
 
 CommandLineHandler::CommandLineHandler()
-    : quit(false)
-    , showedVersion(false)
-    , disableOpenGL(false)
-    , exportMap(false)
-    , exportTileset(false)
-    , newInstance(false)
 {
     option<&CommandLineHandler::showVersion>(
                 QLatin1Char('v'),
@@ -470,18 +466,33 @@ int main(int argc, char *argv[])
         return 0;
     }
 
-    if (!commandLine.filesToOpen().isEmpty() && !commandLine.newInstance) {
-        // Convert files to absolute paths because the already running Tiled
+    QStringList filesToOpen;
+
+    for (const QString &fileName : commandLine.filesToOpen()) {
+        const QFileInfo fileInfo(fileName);
+        const QString filePath = QDir::cleanPath(fileInfo.absoluteFilePath());
+
+        if (fileInfo.suffix() == QLatin1String("tiled-project")) {
+            if (!fileInfo.exists()) {
+                qWarning().noquote() << QCoreApplication::translate("Command line", "Project file '%1' not found.").arg(fileName);
+                return 1;
+            }
+            Preferences::setStartupProject(filePath);
+        } else {
+            filesToOpen.append(filePath);
+        }
+    }
+
+    if (!filesToOpen.isEmpty() && !commandLine.newInstance) {
+        // Files need to be absolute paths because the already running Tiled
         // instance likely does not have the same working directory.
-        QStringList absolutePaths;
-        for (const QString &fileName : commandLine.filesToOpen())
-            absolutePaths.append(QFileInfo(fileName).absoluteFilePath());
-        QJsonDocument doc(QJsonArray::fromStringList(absolutePaths));
+        QJsonDocument doc(QJsonArray::fromStringList(filesToOpen));
         if (a.sendMessage(QLatin1String(doc.toJson())))
             return 0;
     }
 
     StyleHelper::initialize();
+    Session::initialize();
 
     MainWindow w;
     w.show();
@@ -498,9 +509,8 @@ int main(int argc, char *argv[])
 
     w.initializeSession();
 
-    if (!commandLine.filesToOpen().isEmpty())
-        for (const QString &fileName : commandLine.filesToOpen())
-            w.openFile(fileName);
+    for (const QString &fileName : qAsConst(filesToOpen))
+        w.openFile(fileName);
 
     return a.exec();
 }
diff --git a/src/tiled/mainwindow.cpp b/src/tiled/mainwindow.cpp
index 7647fd8942..c61ea4bd74 100644
--- a/src/tiled/mainwindow.cpp
+++ b/src/tiled/mainwindow.cpp
@@ -420,7 +420,7 @@ MainWindow::MainWindow(QWidget *parent, Qt::WindowFlags flags)
     mUi->actionHighlightCurrentLayer->setChecked(preferences->highlightCurrentLayer());
     mUi->actionHighlightHoveredObject->setChecked(preferences->highlightHoveredObject());
 
-    bindToOption(mUi->actionAutoMapWhileDrawing, Preferences::automappingWhileDrawing);
+    bindToOption(mUi->actionAutoMapWhileDrawing, AutomappingManager::automappingWhileDrawing);
 
     mUi->actionHighlightCurrentLayer->setIcon(highlightCurrentLayerIcon);
     mUi->actionHighlightCurrentLayer->setIconVisibleInMenu(false);
@@ -584,7 +584,7 @@ MainWindow::MainWindow(QWidget *parent, Qt::WindowFlags flags)
         if (!WorldManager::instance().loadWorld(worldFile, &errorString))
             QMessageBox::critical(this, tr("Error Loading World"), errorString);
         else
-            Preferences::loadedWorlds = WorldManager::instance().worlds().keys();
+            mLoadedWorlds = WorldManager::instance().worlds().keys();
     });
     connect(mUi->menuUnloadWorld, &QMenu::aboutToShow, this, [this] {
         mUi->menuUnloadWorld->clear();
@@ -599,7 +599,7 @@ MainWindow::MainWindow(QWidget *parent, Qt::WindowFlags flags)
                     return;
 
                 WorldManager::instance().unloadWorld(fileName);
-                Preferences::loadedWorlds = WorldManager::instance().worlds().keys();
+                mLoadedWorlds = WorldManager::instance().worlds().keys();
             });
         }
     });
@@ -620,7 +620,7 @@ MainWindow::MainWindow(QWidget *parent, Qt::WindowFlags flags)
         if (!WorldManager::instance().addEmptyWorld(worldFile, &errorString))
             QMessageBox::critical(this, tr("Error Creating World"), errorString);
         else
-            Preferences::loadedWorlds = WorldManager::instance().worlds().keys();
+            mLoadedWorlds = WorldManager::instance().worlds().keys();
     });
     connect(mUi->menuSaveWorld, &QMenu::aboutToShow, this, [this] {
         mUi->menuSaveWorld->clear();
@@ -810,7 +810,7 @@ MainWindow::MainWindow(QWidget *parent, Qt::WindowFlags flags)
 
 MainWindow::~MainWindow()
 {
-    Preferences::instance()->saveSessionNow();
+    emit Preferences::instance()->aboutToSwitchSession();
 
     mDocumentManager->closeAllDocuments();
     mDocumentManager->deleteEditors();
@@ -914,12 +914,13 @@ void MainWindow::newMap()
 
 void MainWindow::initializeSession()
 {
-    const auto prefs = Preferences::instance();
-    const auto &session = prefs->session();
+    const auto &session = Session::current();
 
     // Restore associated project if applicable
     Project project;
-    if (!session.project.isEmpty() && project.load(session.project)) {
+    bool projectLoaded = !session.project.isEmpty() && project.load(session.project);
+
+    if (projectLoaded) {
         mProjectDock->setProject(std::move(project));
         updateWindowTitle();
     }
@@ -929,7 +930,7 @@ void MainWindow::initializeSession()
     // adding the project's extension path.
     ScriptManager::instance().initialize();
 
-    if (prefs->restoreSessionOnStartup())
+    if (projectLoaded || Preferences::instance()->restoreSessionOnStartup())
         restoreSession();
 }
 
@@ -1304,14 +1305,12 @@ void MainWindow::saveProjectAs()
                               tr("An error occurred while saving the project."));
     }
 
-    prefs->addRecentProject(fileName);
-    prefs->session().project = fileName;
-
-    const auto sessionFileName = Session::defaultFileNameForProject(fileName);
-    prefs->session().setFileName(sessionFileName);
+    Session &session = Session::current();
+    session.setFileName(Session::defaultFileNameForProject(fileName));
+    session.setProject(fileName);
 
-    prefs->saveSessionNow();
-    prefs->setLastSession(sessionFileName);
+    prefs->addRecentProject(fileName);
+    prefs->setLastSession(session.fileName());
 
     updateWindowTitle();
     updateActions();
@@ -1329,22 +1328,21 @@ void MainWindow::closeProject()
 void MainWindow::switchProject(Project project)
 {
     auto prefs = Preferences::instance();
-    prefs->saveSessionNow();
+    emit prefs->aboutToSwitchSession();
 
     if (!closeAllFiles())
         return;
 
     WorldManager::instance().unloadAllWorlds();
 
-    Session session { Session::defaultFileNameForProject(project.fileName()) };
+    auto &session = Session::switchCurrent(Session::defaultFileNameForProject(project.fileName()));
 
     if (!project.fileName().isEmpty()) {
-        session.project = project.fileName();
+        session.setProject(project.fileName());
         prefs->addRecentProject(project.fileName());
     }
 
     mProjectDock->setProject(std::move(project));
-    prefs->switchSession(std::move(session));
 
     ScriptManager::instance().refreshExtensionsPaths();
 
@@ -1355,7 +1353,7 @@ void MainWindow::switchProject(Project project)
 
 void MainWindow::restoreSession()
 {
-    const auto &session = Preferences::instance()->session();
+    const auto &session = Session::current();
 
     // Copy values because the session will get changed while restoring it
     const auto openFiles = session.openFiles;
@@ -1365,7 +1363,7 @@ void MainWindow::restoreSession()
         openFile(file);
     mDocumentManager->switchToDocument(activeFile);
 
-    WorldManager::instance().loadWorlds(Preferences::loadedWorlds);
+    WorldManager::instance().loadWorlds(mLoadedWorlds);
 
     mProjectDock->setExpandedPaths(session.expandedProjectPaths);
 }
@@ -1746,7 +1744,7 @@ void MainWindow::openRecentFile()
 
 void MainWindow::reopenClosedFile()
 {
-    const auto recentFiles = Preferences::instance()->session().recentFiles;
+    const auto &recentFiles = Session::current().recentFiles;
     for (const QString &file : recentFiles) {
         if (mDocumentManager->findDocument(file) == -1) {
             openFile(file);
@@ -1767,7 +1765,7 @@ void MainWindow::openRecentProject()
  */
 void MainWindow::updateRecentFilesMenu()
 {
-    const QStringList files = Preferences::instance()->session().recentFiles;
+    const auto &files = Session::current().recentFiles;
     const int numRecentFiles = qMin<int>(files.size(), Preferences::MaxRecentFiles);
 
     for (int i = 0; i < numRecentFiles; ++i) {
diff --git a/src/tiled/mainwindow.h b/src/tiled/mainwindow.h
index a17732e60c..5ac752a33e 100644
--- a/src/tiled/mainwindow.h
+++ b/src/tiled/mainwindow.h
@@ -28,6 +28,7 @@
 #include "preferences.h"
 #include "preferencesdialog.h"
 #include "project.h"
+#include "session.h"
 
 #include <QMainWindow>
 #include <QPointer>
@@ -246,6 +247,8 @@ class MainWindow : public QMainWindow
 
     QMap<QMainWindow*, QByteArray> mMainWindowStates;
 
+    SessionOption<QStringList> mLoadedWorlds { "loadedWorlds" };
+
     static MainWindow *mInstance;
 };
 
diff --git a/src/tiled/mapeditor.cpp b/src/tiled/mapeditor.cpp
index 16dad6a437..fab6d40d9c 100644
--- a/src/tiled/mapeditor.cpp
+++ b/src/tiled/mapeditor.cpp
@@ -311,7 +311,7 @@ MapEditor::MapEditor(QObject *parent)
     connect(prefs, &Preferences::languageChanged, this, &MapEditor::retranslateUi);
     connect(prefs, &Preferences::showTileCollisionShapesChanged,
             this, &MapEditor::showTileCollisionShapesChanged);
-    connect(prefs, &Preferences::aboutToSaveSession,
+    connect(prefs, &Preferences::aboutToSwitchSession,
             this, [this] { if (mCurrentMapDocument) saveDocumentState(mCurrentMapDocument); });
 
     connect(&WorldManager::instance(), &WorldManager::worldsChanged,
@@ -622,9 +622,7 @@ void MapEditor::saveDocumentState(MapDocument *mapDocument) const
     fileState.insert(QLatin1String("viewCenter"), toSettingsValue(viewCenter));
     fileState.insert(QLatin1String("selectedLayer"), globalIndex(mapDocument->currentLayer()));
 
-    Preferences *prefs = Preferences::instance();
-    prefs->session().setFileState(mapDocument->fileName(), fileState);
-    prefs->saveSession();
+    Session::current().setFileState(mapDocument->fileName(), fileState);
 }
 
 void MapEditor::restoreDocumentState(MapDocument *mapDocument) const
@@ -633,8 +631,7 @@ void MapEditor::restoreDocumentState(MapDocument *mapDocument) const
     if (!mapView)
         return;
 
-    Preferences *prefs = Preferences::instance();
-    const QVariantMap fileState = prefs->session().fileState(mapDocument->fileName());
+    const QVariantMap fileState = Session::current().fileState(mapDocument->fileName());
     if (fileState.isEmpty())
         return;
 
diff --git a/src/tiled/mapscene.cpp b/src/tiled/mapscene.cpp
index 167448e82c..54d18cdf44 100644
--- a/src/tiled/mapscene.cpp
+++ b/src/tiled/mapscene.cpp
@@ -40,6 +40,7 @@
 #include "worldmanager.h"
 
 #include <QApplication>
+#include <QFileInfo>
 #include <QGraphicsSceneMouseEvent>
 #include <QKeyEvent>
 #include <QMimeData>
diff --git a/src/tiled/preferences.cpp b/src/tiled/preferences.cpp
index 9d19f362f2..521c865e1a 100644
--- a/src/tiled/preferences.cpp
+++ b/src/tiled/preferences.cpp
@@ -26,6 +26,7 @@
 #include "mapdocument.h"
 #include "pluginmanager.h"
 #include "savefile.h"
+#include "session.h"
 #include "tilesetmanager.h"
 
 #include <QDir>
@@ -35,10 +36,8 @@
 
 using namespace Tiled;
 
-SessionOption<bool> Preferences::automappingWhileDrawing { "automapping.whileDrawing", false };
-SessionOption<QStringList> Preferences::loadedWorlds { "loadedWorlds" };
-
 Preferences *Preferences::mInstance;
+QString Preferences::mStartupProject;
 
 Preferences *Preferences::instance()
 {
@@ -54,7 +53,6 @@ void Preferences::deleteInstance()
 }
 
 Preferences::Preferences()
-    : mSession(restoreSessionOnStartup() ? lastSession() : Session::defaultFileName())
 {
     // Make sure the data directory exists
     const QDir dataDir { dataLocation() };
@@ -94,81 +92,6 @@ Preferences::Preferences()
 
     Object::setObjectTypes(objectTypes);
 
-    mSaveSessionTimer.setInterval(1000);
-    mSaveSessionTimer.setSingleShot(true);
-    connect(&mSaveSessionTimer, &QTimer::timeout, this, [this] { saveSessionNow(); });
-
-    // Migrate some preferences to the session for compatibility
-    migrateToSession<bool>("Automapping/WhileDrawing", "automapping.whileDrawing");
-
-    migrateToSession<QStringList>("LoadedWorlds", "loadedWorlds");
-    migrateToSession<QString>("Storage/StampsDirectory", "stampsFolder");
-
-    migrateToSession<int>("Map/Orientation", "map.orientation");
-    migrateToSession<int>("Storage/LayerDataFormat", "map.layerDataFormat");
-    migrateToSession<int>("Storage/MapRenderOrder", "map.renderOrder");
-    migrateToSession<bool>("Map/FixedSize", "map.fixedSize");
-    migrateToSession<int>("Map/Width", "map.width");
-    migrateToSession<int>("Map/Height", "map.height");
-    migrateToSession<int>("Map/TileWidth", "map.tileWidth");
-    migrateToSession<int>("Map/TileHeight", "map.tileHeight");
-
-    migrateToSession<int>("Tileset/Type", "tileset.type");
-    migrateToSession<bool>("Tileset/EmbedInMap", "tileset.embedInMap");
-    migrateToSession<bool>("Tileset/UseTransparentColor", "tileset.useTransparentColor");
-    migrateToSession<QColor>("Tileset/TransparentColor", "tileset.transparentColor");
-    migrateToSession<QSize>("Tileset/TileSize", "tileset.tileSize");
-    migrateToSession<int>("Tileset/Spacing", "tileset.spacing");
-    migrateToSession<int>("Tileset/Margin", "tileset.margin");
-
-    migrateToSession<QString>("AddPropertyDialog/PropertyType", "property.type");
-
-    migrateToSession<QStringList>("Console/History", "console.history");
-
-    migrateToSession<bool>("SaveAsImage/VisibleLayersOnly", "exportAsImage.visibleLayersOnly");
-    migrateToSession<bool>("SaveAsImage/CurrentScale", "exportAsImage.useCurrentScale");
-    migrateToSession<bool>("SaveAsImage/DrawGrid", "exportAsImage.drawTileGrid");
-    migrateToSession<bool>("SaveAsImage/IncludeBackgroundColor", "exportAsImage.includeBackgroundColor");
-
-    migrateToSession<bool>("ResizeMap/RemoveObjects", "resizeMap.removeObjects");
-
-    migrateToSession<int>("Animation/FrameDuration", "frame.defaultDuration");
-
-    migrateToSession<QString>("lastUsedExportFilter", "map.lastUsedExportFilter");
-    migrateToSession<QString>("lastUsedMapFormat", "map.lastUsedFormat");
-    migrateToSession<QString>("lastUsedOpenFilter", "file.lastUsedOpenFilter");
-    migrateToSession<QString>("lastUsedTilesetExportFilter", "tileset.lastUsedExportFilter");
-    migrateToSession<QString>("lastUsedTilesetFilter", "tileset.lastUsedFilter");
-    migrateToSession<QString>("lastUsedTilesetFormat", "tileset.lastUsedFormat");
-
-    // Migrate some preferences that need manual handling
-    if (mSession.fileName() == Session::defaultFileName()) {
-        if (contains(QLatin1String("recentFiles"))) {
-            mSession.recentFiles = get<QStringList>("recentFiles/fileNames");
-            mSession.openFiles = get<QStringList>("recentFiles/lastOpenFiles");
-            mSession.activeFile = get<QString>("recentFiles/lastActive");
-        }
-
-        if (contains(QLatin1String("MapEditor/MapStates"))) {
-            const auto mapStates = get<QVariantMap>("MapEditor/MapStates");
-
-            for (auto it = mapStates.begin(); it != mapStates.end(); ++it) {
-                const QString &fileName = it.key();
-                auto mapState = it.value().toMap();
-
-                const QPointF viewCenter = mapState.value(QLatin1String("viewCenter")).toPointF();
-
-                mapState.insert(QLatin1String("viewCenter"), toSettingsValue(viewCenter));
-
-                mSession.setFileState(fileName, mapState);
-            }
-        }
-
-        if (mSession.save()) {
-            remove(QLatin1String("recentFiles"));
-            remove(QLatin1String("MapEditor/MapStates"));
-        }
-    }
 
     TilesetManager *tilesetManager = TilesetManager::instance();
     tilesetManager->setReloadTilesetsOnChange(reloadTilesetsOnChange());
@@ -670,11 +593,12 @@ void Preferences::setDonationDialogReminder(const QDate &date)
 
 QString Preferences::fileDialogStartLocation() const
 {
-    if (!mSession.activeFile.isEmpty())
-        return QFileInfo(mSession.activeFile).path();
+    const auto &session = Session::current();
+    if (!session.activeFile.isEmpty())
+        return QFileInfo(session.activeFile).path();
 
-    if (!mSession.recentFiles.isEmpty())
-        return QFileInfo(mSession.recentFiles.first()).path();
+    if (!session.recentFiles.isEmpty())
+        return QFileInfo(session.recentFiles.first()).path();
 
     return QStandardPaths::writableLocation(QStandardPaths::HomeLocation);
 }
@@ -684,8 +608,7 @@ QString Preferences::fileDialogStartLocation() const
  */
 void Preferences::addRecentFile(const QString &fileName)
 {
-    mSession.addRecentFile(fileName);
-    saveSession();
+    Session::current().addRecentFile(fileName);
     emit recentFilesChanged();
 }
 
@@ -704,8 +627,13 @@ void Preferences::addRecentProject(const QString &fileName)
     emit recentProjectsChanged();
 }
 
-QString Preferences::lastSession() const
+QString Preferences::startupSession() const
 {
+    if (!startupProject().isEmpty())
+        return Session::defaultFileNameForProject(startupProject());
+    if (!restoreSessionOnStartup())
+        return Session::defaultFileName();
+
     const auto session = get<QString>("Project/LastSession");
     return session.isEmpty() ? Session::defaultFileName() : session;
 }
@@ -720,28 +648,6 @@ bool Preferences::restoreSessionOnStartup() const
     return get("Startup/RestorePreviousSession", true);
 }
 
-void Preferences::switchSession(Session session)
-{
-    mSession = std::move(session);
-    setLastSession(mSession.fileName());
-
-    Session::notifySessionChanged();
-    emit recentFilesChanged();
-}
-
-void Preferences::saveSession()
-{
-    if (!mSaveSessionTimer.isActive())
-        mSaveSessionTimer.start();
-}
-
-void Preferences::saveSessionNow()
-{
-    emit aboutToSaveSession();
-    mSaveSessionTimer.stop();
-    mSession.save();
-}
-
 void Preferences::addToRecentFileList(const QString &fileName, QStringList& files)
 {
     // Remember the file by its absolute file path (not the canonical one,
@@ -758,8 +664,7 @@ void Preferences::addToRecentFileList(const QString &fileName, QStringList& file
 
 void Preferences::clearRecentFiles()
 {
-    mSession.recentFiles.clear();
-    saveSession();
+    Session::current().clearRecentFiles();
     emit recentFilesChanged();
 }
 
@@ -846,6 +751,22 @@ QString Preferences::configLocation()
     return QStandardPaths::writableLocation(QStandardPaths::AppConfigLocation);
 }
 
+QString Preferences::startupProject()
+{
+    return mStartupProject;
+}
+
+/**
+ * Sets the project to load on startup (passed on command-line).
+ *
+ * Needs to be set before the Session is initialized, because it determines
+ * the location of the session file.
+ */
+void Preferences::setStartupProject(const QString &filePath)
+{
+    mStartupProject = filePath;
+}
+
 QString Preferences::objectTypesFile() const
 {
     QString file = get<QString>("Storage/ObjectTypesFile");
diff --git a/src/tiled/preferences.h b/src/tiled/preferences.h
index 227ecb31d1..cda8f9da65 100644
--- a/src/tiled/preferences.h
+++ b/src/tiled/preferences.h
@@ -29,7 +29,6 @@
 #include "filesystemwatcher.h"
 #include "map.h"
 #include "objecttypes.h"
-#include "session.h"
 
 namespace Tiled {
 
@@ -165,13 +164,9 @@ class Preferences : public QSettings
     QStringList recentProjects() const;
     void addRecentProject(const QString &fileName);
 
-    QString lastSession() const;
+    QString startupSession() const;
     void setLastSession(const QString &fileName);
-    Session &session();
     bool restoreSessionOnStartup() const;
-    void switchSession(Session session);
-    void saveSession();
-    void saveSessionNow();
 
     bool checkForUpdates() const;
     void setCheckForUpdates(bool on);
@@ -188,8 +183,8 @@ class Preferences : public QSettings
     static QString dataLocation();
     static QString configLocation();
 
-    static SessionOption<bool> automappingWhileDrawing;
-    static SessionOption<QStringList> loadedWorlds;
+    static QString startupProject();
+    static void setStartupProject(const QString &filePath);
 
 public slots:
     void setShowGrid(bool showGrid);
@@ -249,43 +244,22 @@ public slots:
     void checkForUpdatesChanged(bool on);
     void displayNewsChanged(bool on);
 
-    void aboutToSaveSession();
+    void aboutToSwitchSession();
 
 private:
-    template<typename T>
-    void migrateToSession(const char *preferencesKey, const char *sessionKey)
-    {
-        if (mSession.isSet(sessionKey))
-            return;
-
-        const auto value = QSettings::value(QLatin1String(preferencesKey));
-        if (!value.isValid())
-            return;
-
-        mSession.set(sessionKey, value.value<T>());
-    }
-
     void addToRecentFileList(const QString &fileName, QStringList &files);
 
     void objectTypesFileChangedOnDisk();
 
     FileSystemWatcher mWatcher;
 
-    Session mSession;
-    QTimer mSaveSessionTimer;
-
     QDateTime mObjectTypesFileLastSaved;
 
     static Preferences *mInstance;
+    static QString mStartupProject;
 };
 
 
-inline Session &Preferences::session()
-{
-    return mSession;
-}
-
-
 template<typename T>
 class Preference
 {
diff --git a/src/tiled/projectdock.cpp b/src/tiled/projectdock.cpp
index a0a0a6380d..de51ebc19b 100644
--- a/src/tiled/projectdock.cpp
+++ b/src/tiled/projectdock.cpp
@@ -26,6 +26,7 @@
 #include "objecttemplate.h"
 #include "preferences.h"
 #include "projectmodel.h"
+#include "session.h"
 #include "templatemanager.h"
 #include "utils.h"
 
@@ -95,9 +96,8 @@ ProjectDock::ProjectDock(QWidget *parent)
     setWidget(widget);
     retranslateUi();
 
-    auto prefs = Preferences::instance();
-    connect(prefs, &Preferences::aboutToSaveSession,
-            this, [this, prefs] { prefs->session().expandedProjectPaths = mProjectView->expandedPaths(); });
+    connect(Preferences::instance(), &Preferences::aboutToSwitchSession,
+            this, [this] { Session::current().expandedProjectPaths = mProjectView->expandedPaths(); });
 
     connect(mProjectView->selectionModel(), &QItemSelectionModel::currentRowChanged,
             this, &ProjectDock::onCurrentRowChanged);
diff --git a/src/tiled/session.cpp b/src/tiled/session.cpp
index 76a5038473..83358ebeab 100644
--- a/src/tiled/session.cpp
+++ b/src/tiled/session.cpp
@@ -55,6 +55,7 @@ QStringList FileHelper::resolve(const QStringList &fileNames) const
 }
 
 QHash<const char*, Session::Callbacks> Session::mChangedCallbacks;
+std::unique_ptr<Session> Session::mCurrent;
 
 Session::Session(const QString &fileName)
     : FileHelper            { fileName }
@@ -68,10 +69,22 @@ Session::Session(const QString &fileName)
     const auto states = get<QVariantMap>("fileStates");
     for (auto it = states.constBegin(); it != states.constEnd(); ++it)
         fileStates.insert(resolve(it.key()), it.value());
+
+    mSyncSettingsTimer.setInterval(1000);
+    mSyncSettingsTimer.setSingleShot(true);
+    QObject::connect(&mSyncSettingsTimer, &QTimer::timeout, [this] { sync(); });
 }
 
-bool Session::save()
+Session::~Session()
+{
+    if (mSyncSettingsTimer.isActive())
+        sync();
+}
+
+void Session::sync()
 {
+    mSyncSettingsTimer.stop();
+
     set("project",              relative(project));
     set("recentFiles",          relative(recentFiles));
     set("openFiles",            relative(openFiles));
@@ -82,7 +95,11 @@ bool Session::save()
     for (auto it = fileStates.constBegin(); it != fileStates.constEnd(); ++it)
         states.insert(relative(it.key()), it.value());
     set("fileStates", states);
+}
 
+bool Session::save()
+{
+    sync();
     settings->sync();
     return settings->status() == QSettings::NoError;
 }
@@ -94,6 +111,10 @@ bool Session::save()
  */
 void Session::setFileName(const QString &fileName)
 {
+    // Make sure we have no pending changes to save to our old location
+    if (mSyncSettingsTimer.isActive())
+        sync();
+
     auto newSettings = Utils::jsonSettings(fileName);
 
     // Copy over all settings
@@ -104,6 +125,14 @@ void Session::setFileName(const QString &fileName)
     settings = std::move(newSettings);
 
     FileHelper::setFileName(fileName);
+
+    scheduleSync();
+}
+
+void Session::setProject(const QString &fileName)
+{
+    project = fileName;
+    scheduleSync();
 }
 
 void Session::addRecentFile(const QString &fileName)
@@ -118,6 +147,26 @@ void Session::addRecentFile(const QString &fileName)
     recentFiles.prepend(absoluteFilePath);
     while (recentFiles.size() > Preferences::MaxRecentFiles)
         recentFiles.removeLast();
+
+    scheduleSync();
+}
+
+void Session::clearRecentFiles()
+{
+    recentFiles.clear();
+    scheduleSync();
+}
+
+void Session::setOpenFiles(const QStringList &fileNames)
+{
+    openFiles = fileNames;
+    scheduleSync();
+}
+
+void Session::setActiveFile(const QString &fileNames)
+{
+    activeFile = fileNames;
+    scheduleSync();
 }
 
 QVariantMap Session::fileState(const QString &fileName) const
@@ -128,6 +177,7 @@ QVariantMap Session::fileState(const QString &fileName) const
 void Session::setFileState(const QString &fileName, const QVariantMap &fileState)
 {
     fileStates.insert(fileName, fileState);
+    scheduleSync();
 }
 
 QString Session::defaultFileName()
@@ -150,16 +200,128 @@ QString Session::defaultFileNameForProject(const QString &projectFile)
     return sessionFile;
 }
 
+Session &Session::initialize()
+{
+    Q_ASSERT(!mCurrent);
+    return switchCurrent(Preferences::instance()->startupSession());
+}
+
 Session &Session::current()
 {
-    return Preferences::instance()->session();
+    Q_ASSERT(mCurrent);
+    return *mCurrent;
 }
 
-void Session::notifySessionChanged()
+static void migratePreferences();
+
+Session &Session::switchCurrent(const QString &fileName)
 {
+    const bool initialSession = !mCurrent;
+
+    mCurrent = std::make_unique<Session>(fileName);
+    Preferences::instance()->setLastSession(mCurrent->fileName());
+
+    if (initialSession)
+        migratePreferences();
+
+    // Call all registered callbacks because any value may have changed
     for (const auto &callbacks : qAsConst(mChangedCallbacks))
         for (const auto &callback : callbacks)
             callback();
+
+    return *mCurrent;
+}
+
+template<typename T>
+static void migrateToSession(const char *preferencesKey, const char *sessionKey)
+{
+    auto &session = Session::current();
+    if (session.isSet(sessionKey))
+        return;
+
+    const auto value = Preferences::instance()->value(QLatin1String(preferencesKey));
+    if (!value.isValid())
+        return;
+
+    session.set(sessionKey, value.value<T>());
+}
+
+static void migratePreferences()
+{
+    // Migrate some preferences to the session for compatibility
+    migrateToSession<bool>("Automapping/WhileDrawing", "automapping.whileDrawing");
+
+    migrateToSession<QStringList>("LoadedWorlds", "loadedWorlds");
+    migrateToSession<QString>("Storage/StampsDirectory", "stampsFolder");
+
+    migrateToSession<int>("Map/Orientation", "map.orientation");
+    migrateToSession<int>("Storage/LayerDataFormat", "map.layerDataFormat");
+    migrateToSession<int>("Storage/MapRenderOrder", "map.renderOrder");
+    migrateToSession<bool>("Map/FixedSize", "map.fixedSize");
+    migrateToSession<int>("Map/Width", "map.width");
+    migrateToSession<int>("Map/Height", "map.height");
+    migrateToSession<int>("Map/TileWidth", "map.tileWidth");
+    migrateToSession<int>("Map/TileHeight", "map.tileHeight");
+
+    migrateToSession<int>("Tileset/Type", "tileset.type");
+    migrateToSession<bool>("Tileset/EmbedInMap", "tileset.embedInMap");
+    migrateToSession<bool>("Tileset/UseTransparentColor", "tileset.useTransparentColor");
+    migrateToSession<QColor>("Tileset/TransparentColor", "tileset.transparentColor");
+    migrateToSession<QSize>("Tileset/TileSize", "tileset.tileSize");
+    migrateToSession<int>("Tileset/Spacing", "tileset.spacing");
+    migrateToSession<int>("Tileset/Margin", "tileset.margin");
+
+    migrateToSession<QString>("AddPropertyDialog/PropertyType", "property.type");
+
+    migrateToSession<QStringList>("Console/History", "console.history");
+
+    migrateToSession<bool>("SaveAsImage/VisibleLayersOnly", "exportAsImage.visibleLayersOnly");
+    migrateToSession<bool>("SaveAsImage/CurrentScale", "exportAsImage.useCurrentScale");
+    migrateToSession<bool>("SaveAsImage/DrawGrid", "exportAsImage.drawTileGrid");
+    migrateToSession<bool>("SaveAsImage/IncludeBackgroundColor", "exportAsImage.includeBackgroundColor");
+
+    migrateToSession<bool>("ResizeMap/RemoveObjects", "resizeMap.removeObjects");
+
+    migrateToSession<int>("Animation/FrameDuration", "frame.defaultDuration");
+
+    migrateToSession<QString>("lastUsedExportFilter", "map.lastUsedExportFilter");
+    migrateToSession<QString>("lastUsedMapFormat", "map.lastUsedFormat");
+    migrateToSession<QString>("lastUsedOpenFilter", "file.lastUsedOpenFilter");
+    migrateToSession<QString>("lastUsedTilesetExportFilter", "tileset.lastUsedExportFilter");
+    migrateToSession<QString>("lastUsedTilesetFilter", "tileset.lastUsedFilter");
+    migrateToSession<QString>("lastUsedTilesetFormat", "tileset.lastUsedFormat");
+
+    auto &session = Session::current();
+    auto prefs = Preferences::instance();
+
+    // Migrate some preferences that need manual handling
+    if (session.fileName() == Session::defaultFileName()) {
+        if (prefs->contains(QLatin1String("recentFiles"))) {
+            session.recentFiles = prefs->get<QStringList>("recentFiles/fileNames");
+            session.setOpenFiles(prefs->get<QStringList>("recentFiles/lastOpenFiles"));
+            session.setActiveFile(prefs->get<QString>("recentFiles/lastActive"));
+        }
+
+        if (prefs->contains(QLatin1String("MapEditor/MapStates"))) {
+            const auto mapStates = prefs->get<QVariantMap>("MapEditor/MapStates");
+
+            for (auto it = mapStates.begin(); it != mapStates.end(); ++it) {
+                const QString &fileName = it.key();
+                auto mapState = it.value().toMap();
+
+                const QPointF viewCenter = mapState.value(QLatin1String("viewCenter")).toPointF();
+
+                mapState.insert(QLatin1String("viewCenter"), toSettingsValue(viewCenter));
+
+                session.setFileState(fileName, mapState);
+            }
+        }
+
+        if (session.save()) {
+            prefs->remove(QLatin1String("recentFiles"));
+            prefs->remove(QLatin1String("MapEditor/MapStates"));
+        }
+    }
 }
 
 } // namespace Tiled
diff --git a/src/tiled/session.h b/src/tiled/session.h
index c87f93f4d1..cdf9febc8b 100644
--- a/src/tiled/session.h
+++ b/src/tiled/session.h
@@ -27,6 +27,7 @@
 #include <QSettings>
 #include <QSize>
 #include <QStringList>
+#include <QTimer>
 #include <QVariantMap>
 
 #include <memory>
@@ -117,21 +118,31 @@ class Session : protected FileHelper
     std::unique_ptr<QSettings> settings;
 
 public:
-    explicit Session(const QString &fileName = QString());
+    explicit Session(const QString &fileName);
+    ~Session();
 
     bool save();
 
     QString fileName() const;
     void setFileName(const QString &fileName);
 
+    void setProject(const QString &fileName);
+
     void addRecentFile(const QString &fileName);
+    void clearRecentFiles();
+
+    void setOpenFiles(const QStringList &fileNames);
+    void setActiveFile(const QString &fileNames);
 
     QVariantMap fileState(const QString &fileName) const;
     void setFileState(const QString &fileName, const QVariantMap &fileState);
 
     template <typename T>
     T get(const char *key, const T &defaultValue = T()) const
-    { return fromSettingsValue<T>(settings->value(QLatin1String(key), toSettingsValue(defaultValue))); }
+    {
+        return fromSettingsValue<T>(settings->value(QLatin1String(key),
+                                                    toSettingsValue(defaultValue)));
+    }
 
     template <typename T>
     void set(const char *key, const T &value) const
@@ -152,9 +163,10 @@ class Session : protected FileHelper
 
     static QString defaultFileName();
     static QString defaultFileNameForProject(const QString &projectFile);
-    static Session &current();
 
-    static void notifySessionChanged();
+    static Session &initialize();
+    static Session &current();
+    static Session &switchCurrent(const QString &fileName);
 
     QString project;
     QStringList recentFiles;
@@ -170,6 +182,12 @@ class Session : protected FileHelper
 private:
     template<typename T> friend class SessionOption;
 
+    void scheduleSync() { mSyncSettingsTimer.start(); }
+    void sync();
+
+    QTimer mSyncSettingsTimer;
+
+    static std::unique_ptr<Session> mCurrent;
     static QHash<const char*, Callbacks> mChangedCallbacks;
 };