diff --git a/AUTHORS.md b/AUTHORS.md
index c760149274..b0a7d8ef79 100644
--- a/AUTHORS.md
+++ b/AUTHORS.md
@@ -31,6 +31,7 @@ possible:
  * Binh Nguyen
  * Bobby Rauchenberg
  * Brendan McAdams
+ * Brian McKenna
  * Cody Allen
  * Colt Frederickson
  * Dale Wijnand
@@ -98,6 +99,13 @@ possible:
  * yilinwei
  * Zach Abbott
 
+Cats has been heavily inspired by many libraries, including [Scalaz](https://github.com/scalaz/scalaz),
+Haskell's [Prelude](https://hackage.haskell.org/package/base-4.9.0.0/docs/Prelude.html), and others.
+In particular, some Cats code is only a slightly modified version of code originating in
+Scalaz. Therefore, we'd also like to credit and thank all of the
+[Scalaz contributors](https://github.com/scalaz/scalaz/graphs/contributors) for
+their work.
+
 We've tried to include everyone, but if you've made a contribution to
 Cats and are not listed, please feel free to open an issue or pull
 request with your name and contribution.
diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index e554e291e3..d9dab56059 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -131,6 +131,12 @@ Write about type class methods on data structures as described in https://github
 
 Write about https://github.com/typelevel/cats/pull/36#issuecomment-72892359
 
+### Attributions
+
+If your contribution has been derived from or inspired by other work, please
+state this in its ScalaDoc comment and provide proper attribution. When
+possible, include the original authors' names and a link to the original work.
+
 ### Write tests
 
 - Tests for cats-core go into the tests module, under the `cats.tests` package.
diff --git a/core/src/main/scala/cats/FlatMapRec.scala b/core/src/main/scala/cats/FlatMapRec.scala
index 5658b3fe00..c4eb8de942 100644
--- a/core/src/main/scala/cats/FlatMapRec.scala
+++ b/core/src/main/scala/cats/FlatMapRec.scala
@@ -9,6 +9,10 @@ import cats.data.Xor
  *
  * Based on Phil Freeman's
  * [[http://functorial.com/stack-safety-for-free/index.pdf Stack Safety for Free]].
+ *
+ * This Scala implementation of `FlatMapRec` and its usages are derived from
+ * [[https://github.com/scalaz/scalaz/blob/series/7.3.x/core/src/main/scala/scalaz/BindRec.scala Scalaz's BindRec]],
+ * originally written by Brian McKenna.
  */
 @typeclass trait FlatMapRec[F[_]] extends FlatMap[F] {
 
diff --git a/core/src/main/scala/cats/NotNull.scala b/core/src/main/scala/cats/NotNull.scala
index 5cf16b5e02..39dbba6691 100644
--- a/core/src/main/scala/cats/NotNull.scala
+++ b/core/src/main/scala/cats/NotNull.scala
@@ -6,6 +6,12 @@ package cats
  *
  * This can be useful in preventing `Null` from being inferred when a type
  * parameter is omitted.
+ *
+ * This trait is used along with ambiguous implicits to achieve the goal of
+ * preventing inference of `Null`. This ambiguous implicit trick has been used
+ * in the Scala community for some time. [[https://gist.github.com/milessabin/de58f3ba7024d51dcc1a Here]]
+ * is an early example of such a trick being used in a similar way to prevent a
+ * `Nothing` type.
  */
 sealed trait NotNull[A]
 
diff --git a/core/src/main/scala/cats/data/Validated.scala b/core/src/main/scala/cats/data/Validated.scala
index cb7cedd3b2..cce53e1a74 100644
--- a/core/src/main/scala/cats/data/Validated.scala
+++ b/core/src/main/scala/cats/data/Validated.scala
@@ -354,6 +354,10 @@ trait ValidatedFunctions {
    * scala> Validated.catchOnly[NumberFormatException] { "foo".toInt }
    * res0: Validated[NumberFormatException, Int] = Invalid(java.lang.NumberFormatException: For input string: "foo")
    * }}}
+   *
+   * This method and its usage of [[NotNull]] are inspired by and derived from
+   * the `fromTryCatchThrowable` method [[https://github.com/scalaz/scalaz/pull/746/files contributed]]
+   * to Scalaz by Brian McKenna.
    */
   def catchOnly[T >: Null <: Throwable]: CatchOnlyPartiallyApplied[T] = new CatchOnlyPartiallyApplied[T]
 
diff --git a/core/src/main/scala/cats/data/Xor.scala b/core/src/main/scala/cats/data/Xor.scala
index b7e599063d..fd253ecb61 100644
--- a/core/src/main/scala/cats/data/Xor.scala
+++ b/core/src/main/scala/cats/data/Xor.scala
@@ -322,6 +322,10 @@ trait XorFunctions {
    * scala> Xor.catchOnly[NumberFormatException] { "foo".toInt }
    * res0: Xor[NumberFormatException, Int] = Left(java.lang.NumberFormatException: For input string: "foo")
    * }}}
+   *
+   * This method and its usage of [[NotNull]] are inspired by and derived from
+   * the `fromTryCatchThrowable` method [[https://github.com/scalaz/scalaz/pull/746/files contributed]]
+   * to Scalaz by Brian McKenna.
    */
   def catchOnly[T >: Null <: Throwable]: CatchOnlyPartiallyApplied[T] =
     new CatchOnlyPartiallyApplied[T]