diff --git a/packages/react-debug-tools/src/ReactDebugHooks.js b/packages/react-debug-tools/src/ReactDebugHooks.js
index ecfcc30d4bad0..612cba9d063d6 100644
--- a/packages/react-debug-tools/src/ReactDebugHooks.js
+++ b/packages/react-debug-tools/src/ReactDebugHooks.js
@@ -114,9 +114,9 @@ function readContext<T>(context: ReactContext<T>): T {
   return context._currentValue;
 }
 
-function useContext<T, S>(
+function useContext<T>(
   context: ReactContext<T>,
-  options?: {unstable_selector?: T => S},
+  options?: {unstable_selector?: T => mixed},
 ): T {
   hookLog.push({
     primitive: 'Context',
diff --git a/packages/react-dom/src/server/ReactPartialRendererHooks.js b/packages/react-dom/src/server/ReactPartialRendererHooks.js
index b692733f52fdf..a7219c58a8779 100644
--- a/packages/react-dom/src/server/ReactPartialRendererHooks.js
+++ b/packages/react-dom/src/server/ReactPartialRendererHooks.js
@@ -235,9 +235,9 @@ function readContext<T>(context: ReactContext<T>): T {
   return context[threadID];
 }
 
-function useContext<T, S>(
+function useContext<T>(
   context: ReactContext<T>,
-  options?: {unstable_selector?: T => S},
+  options?: {unstable_selector?: T => mixed},
 ): T {
   if (__DEV__) {
     currentHookNameInDev = 'useContext';
diff --git a/packages/react-reconciler/src/ReactFiberHooks.new.js b/packages/react-reconciler/src/ReactFiberHooks.new.js
index bfabfb51f8d72..18d34bc6c3a8e 100644
--- a/packages/react-reconciler/src/ReactFiberHooks.new.js
+++ b/packages/react-reconciler/src/ReactFiberHooks.new.js
@@ -680,9 +680,9 @@ function updateWorkInProgressHook(): Hook {
   return workInProgressHook;
 }
 
-function useContext<T, S>(
+function useContext<T>(
   context: ReactContext<T>,
-  options?: {unstable_selector?: T => S},
+  options?: {unstable_selector?: T => mixed},
 ): T {
   if (options !== undefined) {
     const selector = options.unstable_selector;
@@ -2216,9 +2216,9 @@ if (__DEV__) {
       checkDepsAreArrayDev(deps);
       return mountCallback(callback, deps);
     },
-    useContext<T, S>(
+    useContext<T>(
       context: ReactContext<T>,
-      options?: {unstable_selector?: T => S},
+      options?: {unstable_selector?: T => mixed},
     ): T {
       currentHookNameInDev = 'useContext';
       mountHookTypesDev();
@@ -2347,9 +2347,9 @@ if (__DEV__) {
       updateHookTypesDev();
       return mountCallback(callback, deps);
     },
-    useContext<T, S>(
+    useContext<T>(
       context: ReactContext<T>,
-      options?: {unstable_selector?: T => S},
+      options?: {unstable_selector?: T => mixed},
     ): T {
       currentHookNameInDev = 'useContext';
       updateHookTypesDev();
@@ -2474,9 +2474,9 @@ if (__DEV__) {
       updateHookTypesDev();
       return updateCallback(callback, deps);
     },
-    useContext<T, S>(
+    useContext<T>(
       context: ReactContext<T>,
-      options?: {unstable_selector?: T => S},
+      options?: {unstable_selector?: T => mixed},
     ): T {
       currentHookNameInDev = 'useContext';
       updateHookTypesDev();
@@ -2602,9 +2602,9 @@ if (__DEV__) {
       updateHookTypesDev();
       return updateCallback(callback, deps);
     },
-    useContext<T, S>(
+    useContext<T>(
       context: ReactContext<T>,
-      options?: {unstable_selector?: T => S},
+      options?: {unstable_selector?: T => mixed},
     ): T {
       currentHookNameInDev = 'useContext';
       updateHookTypesDev();
@@ -2731,9 +2731,9 @@ if (__DEV__) {
       mountHookTypesDev();
       return mountCallback(callback, deps);
     },
-    useContext<T, S>(
+    useContext<T>(
       context: ReactContext<T>,
-      options?: {unstable_selector?: T => S},
+      options?: {unstable_selector?: T => mixed},
     ): T {
       currentHookNameInDev = 'useContext';
       warnInvalidHookAccess();
@@ -2873,9 +2873,9 @@ if (__DEV__) {
       updateHookTypesDev();
       return updateCallback(callback, deps);
     },
-    useContext<T, S>(
+    useContext<T>(
       context: ReactContext<T>,
-      options?: {unstable_selector?: T => S},
+      options?: {unstable_selector?: T => mixed},
     ): T {
       currentHookNameInDev = 'useContext';
       warnInvalidHookAccess();
@@ -3016,9 +3016,9 @@ if (__DEV__) {
       updateHookTypesDev();
       return updateCallback(callback, deps);
     },
-    useContext<T, S>(
+    useContext<T>(
       context: ReactContext<T>,
-      options?: {unstable_selector?: T => S},
+      options?: {unstable_selector?: T => mixed},
     ): T {
       currentHookNameInDev = 'useContext';
       warnInvalidHookAccess();
diff --git a/packages/react-reconciler/src/ReactFiberHooks.old.js b/packages/react-reconciler/src/ReactFiberHooks.old.js
index 374ebb08299ac..d90e5f1fbf76a 100644
--- a/packages/react-reconciler/src/ReactFiberHooks.old.js
+++ b/packages/react-reconciler/src/ReactFiberHooks.old.js
@@ -680,9 +680,9 @@ function updateWorkInProgressHook(): Hook {
   return workInProgressHook;
 }
 
-function useContext<T, S>(
+function useContext<T>(
   context: ReactContext<T>,
-  options?: {unstable_selector?: T => S},
+  options?: {unstable_selector?: T => mixed},
 ): T {
   if (options !== undefined) {
     const selector = options.unstable_selector;
@@ -2216,9 +2216,9 @@ if (__DEV__) {
       checkDepsAreArrayDev(deps);
       return mountCallback(callback, deps);
     },
-    useContext<T, S>(
+    useContext<T>(
       context: ReactContext<T>,
-      options?: {unstable_selector?: T => S},
+      options?: {unstable_selector?: T => mixed},
     ): T {
       currentHookNameInDev = 'useContext';
       mountHookTypesDev();
@@ -2347,9 +2347,9 @@ if (__DEV__) {
       updateHookTypesDev();
       return mountCallback(callback, deps);
     },
-    useContext<T, S>(
+    useContext<T>(
       context: ReactContext<T>,
-      options?: {unstable_selector?: T => S},
+      options?: {unstable_selector?: T => mixed},
     ): T {
       currentHookNameInDev = 'useContext';
       updateHookTypesDev();
@@ -2474,9 +2474,9 @@ if (__DEV__) {
       updateHookTypesDev();
       return updateCallback(callback, deps);
     },
-    useContext<T, S>(
+    useContext<T>(
       context: ReactContext<T>,
-      options?: {unstable_selector?: T => S},
+      options?: {unstable_selector?: T => mixed},
     ): T {
       currentHookNameInDev = 'useContext';
       updateHookTypesDev();
@@ -2602,9 +2602,9 @@ if (__DEV__) {
       updateHookTypesDev();
       return updateCallback(callback, deps);
     },
-    useContext<T, S>(
+    useContext<T>(
       context: ReactContext<T>,
-      options?: {unstable_selector?: T => S},
+      options?: {unstable_selector?: T => mixed},
     ): T {
       currentHookNameInDev = 'useContext';
       updateHookTypesDev();
@@ -2731,9 +2731,9 @@ if (__DEV__) {
       mountHookTypesDev();
       return mountCallback(callback, deps);
     },
-    useContext<T, S>(
+    useContext<T>(
       context: ReactContext<T>,
-      options?: {unstable_selector?: T => S},
+      options?: {unstable_selector?: T => mixed},
     ): T {
       currentHookNameInDev = 'useContext';
       warnInvalidHookAccess();
@@ -2873,9 +2873,9 @@ if (__DEV__) {
       updateHookTypesDev();
       return updateCallback(callback, deps);
     },
-    useContext<T, S>(
+    useContext<T>(
       context: ReactContext<T>,
-      options?: {unstable_selector?: T => S},
+      options?: {unstable_selector?: T => mixed},
     ): T {
       currentHookNameInDev = 'useContext';
       warnInvalidHookAccess();
@@ -3016,9 +3016,9 @@ if (__DEV__) {
       updateHookTypesDev();
       return updateCallback(callback, deps);
     },
-    useContext<T, S>(
+    useContext<T>(
       context: ReactContext<T>,
-      options?: {unstable_selector?: T => S},
+      options?: {unstable_selector?: T => mixed},
     ): T {
       currentHookNameInDev = 'useContext';
       warnInvalidHookAccess();
diff --git a/packages/react-reconciler/src/ReactFiberNewContext.new.js b/packages/react-reconciler/src/ReactFiberNewContext.new.js
index f208942b8fbf0..b5a564042ce7b 100644
--- a/packages/react-reconciler/src/ReactFiberNewContext.new.js
+++ b/packages/react-reconciler/src/ReactFiberNewContext.new.js
@@ -212,7 +212,6 @@ function propagateContextChange_eager<T>(
       let dependency = list.firstContext;
       while (dependency !== null) {
         // Check if the context matches.
-        // TODO: Compare selected values to bail out early.
         if (dependency.context === context) {
           // Match! Schedule an update on this fiber.
           if (fiber.tag === ClassComponent) {
@@ -348,8 +347,19 @@ function propagateContextChanges<T>(
         findContext: for (let i = 0; i < contexts.length; i++) {
           const context: ReactContext<T> = contexts[i];
           // Check if the context matches.
-          // TODO: Compare selected values to bail out early.
           if (dependency.context === context) {
+            const selector = dependency.selector;
+            if (selector !== null) {
+              const newValue = isPrimaryRenderer
+                ? context._currentValue
+                : context._currentValue2;
+              const newSelectedValue = selector(newValue);
+              const oldSelectedValue = dependency.selectedValue;
+              if (is(oldSelectedValue, selector(newSelectedValue))) {
+                // Selected value hasn't changed. Bail out early.
+                continue findContext;
+              }
+            }
             // Match! Schedule an update on this fiber.
 
             // In the lazy implemenation, don't mark a dirty flag on the
@@ -571,10 +581,8 @@ export function checkIfContextChanged(currentDependencies: Dependencies) {
     const oldValue = dependency.memoizedValue;
     const selector = dependency.selector;
     if (selector !== null) {
-      // TODO: Alternatively, we could store the selected value on the context.
-      // However, we expect selectors to do nothing except access a subfield,
-      // so this is probably fine, too.
-      if (!is(selector(newValue), selector(oldValue))) {
+      const oldSelectedValue = dependency.selectedValue;
+      if (!is(selector(newValue), oldSelectedValue)) {
         return true;
       }
     } else {
@@ -657,8 +665,11 @@ function readContextImpl<C, S>(
     const contextItem = {
       context: ((context: any): ReactContext<mixed>),
       selector: ((selector: any): ContextSelector<mixed, mixed> | null),
-      // TODO: Store selected value so we can compare to that during propagation
       memoizedValue: value,
+      // TODO: If useContextSelector becomes a built-in API, then
+      // readContextWithSelector should return the selected value so that we
+      // don't call the selector twice. Will need to inline readContextImpl.
+      selectedValue: selector !== null ? selector(value) : null,
       next: null,
     };
 
diff --git a/packages/react-reconciler/src/ReactFiberNewContext.old.js b/packages/react-reconciler/src/ReactFiberNewContext.old.js
index 6dfb0732fd2f7..da37ae511238d 100644
--- a/packages/react-reconciler/src/ReactFiberNewContext.old.js
+++ b/packages/react-reconciler/src/ReactFiberNewContext.old.js
@@ -212,7 +212,6 @@ function propagateContextChange_eager<T>(
       let dependency = list.firstContext;
       while (dependency !== null) {
         // Check if the context matches.
-        // TODO: Compare selected values to bail out early.
         if (dependency.context === context) {
           // Match! Schedule an update on this fiber.
           if (fiber.tag === ClassComponent) {
@@ -348,8 +347,19 @@ function propagateContextChanges<T>(
         findContext: for (let i = 0; i < contexts.length; i++) {
           const context: ReactContext<T> = contexts[i];
           // Check if the context matches.
-          // TODO: Compare selected values to bail out early.
           if (dependency.context === context) {
+            const selector = dependency.selector;
+            if (selector !== null) {
+              const newValue = isPrimaryRenderer
+                ? context._currentValue
+                : context._currentValue2;
+              const newSelectedValue = selector(newValue);
+              const oldSelectedValue = dependency.selectedValue;
+              if (is(oldSelectedValue, selector(newSelectedValue))) {
+                // Selected value hasn't changed. Bail out early.
+                continue findContext;
+              }
+            }
             // Match! Schedule an update on this fiber.
 
             // In the lazy implemenation, don't mark a dirty flag on the
@@ -571,10 +581,8 @@ export function checkIfContextChanged(currentDependencies: Dependencies) {
     const oldValue = dependency.memoizedValue;
     const selector = dependency.selector;
     if (selector !== null) {
-      // TODO: Alternatively, we could store the selected value on the context.
-      // However, we expect selectors to do nothing except access a subfield,
-      // so this is probably fine, too.
-      if (!is(selector(newValue), selector(oldValue))) {
+      const oldSelectedValue = dependency.selectedValue;
+      if (!is(selector(newValue), oldSelectedValue)) {
         return true;
       }
     } else {
@@ -657,8 +665,11 @@ function readContextImpl<C, S>(
     const contextItem = {
       context: ((context: any): ReactContext<mixed>),
       selector: ((selector: any): ContextSelector<mixed, mixed> | null),
-      // TODO: Store selected value so we can compare to that during propagation
       memoizedValue: value,
+      // TODO: If useContextSelector becomes a built-in API, then
+      // readContextWithSelector should return the selected value so that we
+      // don't call the selector twice. Will need to inline readContextImpl.
+      selectedValue: selector !== null ? selector(value) : null,
       next: null,
     };
 
diff --git a/packages/react-reconciler/src/ReactInternalTypes.js b/packages/react-reconciler/src/ReactInternalTypes.js
index ea7a542942bf1..524703db00093 100644
--- a/packages/react-reconciler/src/ReactInternalTypes.js
+++ b/packages/react-reconciler/src/ReactInternalTypes.js
@@ -51,6 +51,7 @@ export type ContextDependency<C, S> = {
   selector: (C => S) | null,
   next: ContextDependency<mixed, mixed> | null,
   memoizedValue: C,
+  selectedValue: S | null,
   ...
 };
 
@@ -282,9 +283,9 @@ export type Dispatcher = {|
     initialArg: I,
     init?: (I) => S,
   ): [S, Dispatch<A>],
-  useContext<T, S>(
+  useContext<T>(
     context: ReactContext<T>,
-    options?: {unstable_selector?: T => S},
+    options?: {unstable_selector?: T => mixed},
   ): T,
   useRef<T>(initialValue: T): {|current: T|},
   useEffect(
diff --git a/packages/react/src/ReactHooks.js b/packages/react/src/ReactHooks.js
index 3518bade21f9d..5794c7d0d99e3 100644
--- a/packages/react/src/ReactHooks.js
+++ b/packages/react/src/ReactHooks.js
@@ -47,9 +47,9 @@ export function getCacheForType<T>(resourceType: () => T): T {
   return dispatcher.getCacheForType(resourceType);
 }
 
-export function useContext<T, S>(
+export function useContext<T>(
   Context: ReactContext<T>,
-  options?: {unstable_selector?: T => S},
+  options?: {unstable_selector?: T => mixed},
 ): T {
   const dispatcher = resolveDispatcher();
   if (__DEV__) {