diff --git a/CHANGES.md b/CHANGES.md
index 17ae711d6..ea6a9a66c 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -3,8 +3,10 @@
 ## Unreleased - 2021-xx-xx
 ### Changed
 * Change compression algorithm features flags. [#2250]
+* Deprecate `App::data` and `App::data_factory`. [#????]
 
 [#2250]: https://github.com/actix/actix-web/pull/2250
+[#????]: https://github.com/actix/actix-web/pull/????
 
 
 ## 4.0.0-beta.7 - 2021-06-17
diff --git a/src/app.rs b/src/app.rs
index 357d45eeb..6eb7a4911 100644
--- a/src/app.rs
+++ b/src/app.rs
@@ -98,13 +98,18 @@ where
     ///         web::resource("/index.html").route(
     ///             web::get().to(index)));
     /// ```
+    #[deprecated(since = "4.0.0", note = "Use `.app_data(Data::new(val))` instead.")]
     pub fn data<U: 'static>(self, data: U) -> Self {
         self.app_data(Data::new(data))
     }
 
-    /// Set application data factory. This function is
-    /// similar to `.data()` but it accepts data factory. Data object get
-    /// constructed asynchronously during application initialization.
+    /// Add application data factory. This function is similar to `.data()` but it accepts a
+    /// "data factory". Data values are constructed asynchronously during application
+    /// initialization, before the server starts accepting requests.
+    #[deprecated(
+        since = "4.0.0",
+        note = "Construct data value before starting server and use `.app_data(Data::new(val))` instead."
+    )]
     pub fn data_factory<F, Out, D, E>(mut self, data: F) -> Self
     where
         F: Fn() -> Out + 'static,