diff --git a/.changeset/add-nested-namespaces.md b/.changeset/add-nested-namespaces.md
new file mode 100644
index 0000000000..39097c49bf
--- /dev/null
+++ b/.changeset/add-nested-namespaces.md
@@ -0,0 +1,17 @@
+---
+'@mermaid': patch
+---
+
+Fixed an issue when the mermaid classdiagram crashes when adding a . to the namespace.
+Forexample
+
+```mermaid
+
+classDiagram
+  namespace Company.Project.Module {
+    class GenericClass~T~ {
+      +addItem(item: T)
+      +getItem() T
+    }
+  }
+```
diff --git a/cypress/integration/rendering/classDiagram-v2.spec.js b/cypress/integration/rendering/classDiagram-v2.spec.js
index 258f8529f6..0c5dbc04b0 100644
--- a/cypress/integration/rendering/classDiagram-v2.spec.js
+++ b/cypress/integration/rendering/classDiagram-v2.spec.js
@@ -581,4 +581,63 @@ class C13["With Città foreign language"]
       { logLevel: 1, flowchart: { htmlLabels: false } }
     );
   });
+
+  it('renders a class diagram with a generic class in a namespace', () => {
+    const diagramDefinition = `
+      classDiagram-v2
+      namespace Company.Project.Module {
+        class GenericClass~T~ {
+          +addItem(item: T)
+          +getItem() T
+        }
+      }
+    `;
+
+    imgSnapshotTest(diagramDefinition);
+  });
+
+  it('renders a class diagram with nested namespaces and relationships', () => {
+    const diagramDefinition = `
+      classDiagram-v2
+      namespace Company.Project.Module.SubModule {
+        class Report {
+          +generatePDF(data: List)
+          +generateCSV(data: List)
+        }
+      }
+      namespace Company.Project.Module {
+        class Admin {
+          +generateReport()
+        }
+      }
+      Admin --> Report : generates
+    `;
+
+    imgSnapshotTest(diagramDefinition);
+  });
+
+  it('renders a class diagram with multiple classes and relationships in a namespace', () => {
+    const diagramDefinition = `
+      classDiagram-v2
+      namespace Company.Project.Module {
+        class User {
+          +login(username: String, password: String)
+          +logout()
+        }
+        class Admin {
+          +addUser(user: User)
+          +removeUser(user: User)
+          +generateReport()
+        }
+        class Report {
+          +generatePDF(reportData: List)
+          +generateCSV(reportData: List)
+        }
+      }
+      Admin --> User : manages
+      Admin --> Report : generates
+    `;
+
+    imgSnapshotTest(diagramDefinition);
+  });
 });
diff --git a/demos/classchart.html b/demos/classchart.html
index f04fa5b5f9..980ea5098d 100644
--- a/demos/classchart.html
+++ b/demos/classchart.html
@@ -159,30 +159,87 @@ <h1>Class diagram demos</h1>
       class People List~List~Person~~
     </pre>
     <hr />
-
     <pre class="mermaid">
     classDiagram
-      A1 --> B1
-      namespace A {
-        class A1 {
-          +foo : string
+      namespace Company.Project.Module {
+        class GenericClass~T~ {
+          +addItem(item: T)
+          +getItem() T
+        }
+      }
+    </pre>
+    <hr />
+    <pre class="mermaid">
+    classDiagram
+      namespace Company.Project.Module.SubModule {
+        class Report {
+          +generatePDF(data: List)
+          +generateCSV(data: List)
         }
-        class A2 {
-          +bar : int
+      }
+      namespace Company.Project.Module {
+        class Admin {
+          +generateReport()
         }
       }
-      namespace B {
-        class B1 {
-          +foo : bool
+      Admin --> Report : generates
+    </pre>
+    <pre class="mermaid">
+    classDiagram
+      namespace Company.Project.Module {
+        class User {
+          +login(username: String, password: String)
+          +logout()
+        }
+        class Admin {
+          +addUser(user: User)
+          +removeUser(user: User)
+          +generateReport()
         }
-        class B2 {
-          +bar : float
+        class Report {
+          +generatePDF(reportData: List)
+          +generateCSV(reportData: List)
         }
       }
-      A2 --> B2
+      Admin --> User : manages
+      Admin --> Report : generates
     </pre>
     <hr />
-
+    <pre class="mermaid">
+    classDiagram
+      namespace Shapes {
+        class Shape {
+          +calculateArea() double
+        }
+        class Circle {
+          +double radius
+        }
+        class Square {
+          +double side
+        }
+      }
+      
+      Shape <|-- Circle
+      Shape <|-- Square
+      
+      namespace Vehicles {
+        class Vehicle {
+          +String brand
+        }
+        class Car {
+          +int horsepower
+        }
+        class Bike {
+          +boolean hasGears
+        }
+      }
+      
+      Vehicle <|-- Car
+      Vehicle <|-- Bike
+      Car --> Circle : "Logo Shape"
+      Bike --> Square : "Logo Shape"
+                  
+    </pre>
     <script type="module">
       import mermaid from './mermaid.esm.mjs';
       mermaid.initialize({
diff --git a/packages/mermaid/src/diagrams/class/classDiagram.spec.ts b/packages/mermaid/src/diagrams/class/classDiagram.spec.ts
index 9804b325ef..41cec8820c 100644
--- a/packages/mermaid/src/diagrams/class/classDiagram.spec.ts
+++ b/packages/mermaid/src/diagrams/class/classDiagram.spec.ts
@@ -14,6 +14,78 @@ describe('given a basic class diagram, ', function () {
       classDb.clear();
       parser.yy = classDb;
     });
+    it('should handle classes within namespaces', () => {
+      const str = `classDiagram
+        namespace Company.Project {
+          class User {
+            +login(username: String, password: String)
+            +logout()
+          }
+        }
+        namespace Company.Project.Module {
+          class Admin {
+            +addUser(user: User)
+            +removeUser(user: User)
+          }
+        }`;
+
+      parser.parse(str);
+
+      const user = classDb.getClass('User');
+      const admin = classDb.getClass('Admin');
+
+      // Check if the classes are correctly registered under their respective namespaces
+      expect(user.parent).toBe('Company.Project');
+      expect(admin.parent).toBe('Company.Project.Module');
+      expect(user.methods.length).toBe(2);
+      expect(admin.methods.length).toBe(2);
+    });
+
+    it('should handle generic classes within namespaces', () => {
+      const str = `classDiagram
+    namespace Company.Project.Module {
+        class GenericClass~T~ {
+            +addItem(item: T)
+            +getItem() T
+        }
+    }`;
+
+      parser.parse(str);
+
+      const genericClass = classDb.getClass('GenericClass');
+      expect(genericClass.type).toBe('T');
+      expect(genericClass.methods[0].getDisplayDetails().displayText).toBe('+addItem(item: T)');
+      expect(genericClass.methods[1].getDisplayDetails().displayText).toBe('+getItem() : T');
+    });
+
+    it('should handle nested namespaces and relationships', () => {
+      const str = `      classDiagram
+        namespace Company.Project.Module.SubModule {
+          class Report {
+            +generatePDF(data: List)
+            +generateCSV(data: List)
+          }
+        }
+        namespace Company.Project.Module {
+          class Admin {
+            +generateReport()
+          }
+        }
+        Admin --> Report : generates`;
+
+      parser.parse(str);
+
+      const report = classDb.getClass('Report');
+      const admin = classDb.getClass('Admin');
+      const relations = classDb.getRelations();
+
+      expect(report.parent).toBe('Company.Project.Module.SubModule');
+      expect(admin.parent).toBe('Company.Project.Module');
+      expect(relations[0].id1).toBe('Admin');
+      expect(relations[0].id2).toBe('Report');
+      expect(relations[0].title).toBe('generates');
+    });
+
     it('should handle accTitle and accDescr', function () {
       const str = `classDiagram
             accTitle: My Title
@@ -48,6 +120,22 @@ describe('given a basic class diagram, ', function () {
       }
     });
 
+    it('should handle fully qualified class names in relationships', () => {
+      const str = `classDiagram
+        namespace Company.Project.Module {
+          class User
+          class Admin
+        }
+          Admin --> User : manages`;
+
+      parser.parse(str);
+
+      const relations = classDb.getRelations();
+      expect(relations[0].id1).toBe('Admin');
+      expect(relations[0].id2).toBe('User');
+      expect(relations[0].title).toBe('manages');
+    });
+
     it('should handle backquoted class names', function () {
       const str = 'classDiagram\n' + 'class `Car`';
 
@@ -393,27 +481,23 @@ class C13["With Città foreign language"]
           Student "1" --o "1" IdCard : carries
           Student "1" --o "1" Bike : rides`);
 
+      const studentClass = classDb.getClasses().get('Student');
+      // Check that the important properties match, but ignore the domId
+      expect(studentClass).toMatchObject({
+        id: 'Student',
+        label: 'Student',
+        members: [
+          expect.objectContaining({
+            id: 'idCard : IdCard',
+            visibility: '-',
+          }),
+        ],
+        methods: [],
+        annotations: [],
+        cssClasses: [],
+      });
+
       expect(classDb.getClasses().size).toBe(3);
-      expect(classDb.getClasses().get('Student')).toMatchInlineSnapshot(`
-        {
-          "annotations": [],
-          "cssClasses": [],
-          "domId": "classId-Student-134",
-          "id": "Student",
-          "label": "Student",
-          "members": [
-            ClassMember {
-              "classifier": "",
-              "id": "idCard : IdCard",
-              "memberType": "attribute",
-              "visibility": "-",
-            },
-          ],
-          "methods": [],
-          "styles": [],
-          "type": "",
-        }
-      `);
       expect(classDb.getRelations().length).toBe(2);
       expect(classDb.getRelations()).toMatchInlineSnapshot(`
         [
diff --git a/packages/mermaid/src/diagrams/class/parser/classDiagram.jison b/packages/mermaid/src/diagrams/class/parser/classDiagram.jison
index ed4e72027f..5fcea2da3c 100644
--- a/packages/mermaid/src/diagrams/class/parser/classDiagram.jison
+++ b/packages/mermaid/src/diagrams/class/parser/classDiagram.jison
@@ -241,11 +241,13 @@ classLabel
 
 namespaceName
     : alphaNumToken { $$=$1; }
+    | alphaNumToken DOT namespaceName { $$=$1+'.'+$3; }
     | alphaNumToken namespaceName { $$=$1+$2; }
     ;
 
 className
     : alphaNumToken { $$=$1; }
+    | alphaNumToken DOT className { $$=$1+'.'+$3; }
     | classLiteralName { $$=$1; }
     | alphaNumToken className { $$=$1+$2; }
     | alphaNumToken GENERICTYPE { $$=$1+'~'+$2+'~'; }
@@ -270,12 +272,12 @@ statement
     ;
 
 namespaceStatement
-    : namespaceIdentifier STRUCT_START classStatements STRUCT_STOP          {yy.addClassesToNamespace($1, $3);}
-    | namespaceIdentifier STRUCT_START NEWLINE classStatements STRUCT_STOP  {yy.addClassesToNamespace($1, $4);}
+    : namespaceIdentifier STRUCT_START classStatements STRUCT_STOP          { yy.addClassesToNamespace($1, $3); }
+    | namespaceIdentifier STRUCT_START NEWLINE classStatements STRUCT_STOP  { yy.addClassesToNamespace($1, $4); }
     ;
 
 namespaceIdentifier
-    : NAMESPACE namespaceName   {$$=$2; yy.addNamespace($2);}
+    : NAMESPACE namespaceName { $$=$2; yy.addNamespace($2); }
     ;
 
 classStatements