diff --git a/build-system/compile/bundles.config.js b/build-system/compile/bundles.config.js
index c8a090983287..62e520868734 100644
--- a/build-system/compile/bundles.config.js
+++ b/build-system/compile/bundles.config.js
@@ -27,7 +27,7 @@ const {VERSION: internalRuntimeVersion} = require('./internal-version');
 exports.jsBundles = {
   'polyfills.js': {
     srcDir: './src/',
-    srcFilename: 'polyfills.js',
+    srcFilename: 'polyfills/index.js',
     destDir: './build/',
     minifiedDestDir: './build/',
   },
diff --git a/build-system/compile/compile.js b/build-system/compile/compile.js
index 577f4622ebf6..b548916a71d1 100644
--- a/build-system/compile/compile.js
+++ b/build-system/compile/compile.js
@@ -154,13 +154,13 @@ function getSrcs(entryModuleFilenames, outputDir, outputFilename, options) {
   // this works fine.
   if (options.includePolyfills) {
     srcs.push(
-      '!build/fake-module/src/polyfills.js',
+      '!build/fake-module/src/polyfills/index.js',
       '!build/fake-module/src/polyfills/**/*.js',
       '!build/fake-polyfills/**/*.js'
     );
   } else {
-    srcs.push('!src/polyfills.js', '!build/fake-polyfills/**/*.js');
-    unneededFiles.push('build/fake-module/src/polyfills.js');
+    srcs.push('!src/polyfills/index.js', '!build/fake-polyfills/**/*.js');
+    unneededFiles.push('build/fake-module/src/polyfills/index.js');
   }
   // Negative globstars must come at the end.
   srcs.push(
@@ -248,7 +248,7 @@ function generateCompilerOptions(outputDir, outputFilename, options) {
     language_out: argv.esm || argv.sxg ? 'NO_TRANSPILE' : 'ECMASCRIPT5_STRICT',
     // We do not use the polyfills provided by closure compiler.
     // If you need a polyfill. Manually include them in the
-    // respective top level polyfills.js files.
+    // respective top level polyfills/*.js files.
     rewrite_polyfills: false,
     externs,
     js_module_root: [
diff --git a/build-system/tasks/check-sourcemaps.js b/build-system/tasks/check-sourcemaps.js
index 991500d9fc7d..22eb66d0c5a3 100644
--- a/build-system/tasks/check-sourcemaps.js
+++ b/build-system/tasks/check-sourcemaps.js
@@ -110,9 +110,9 @@ function checkSourcemapSources(sourcemapJson, map) {
  * Performs a sanity check on the mappings field in the sourcemap file.
  *
  * Today, the first line of amp.js after resolving imports comes from
- * src/polyfills/array-includes.js. (The import chain is src/amp.js -> src/polyfills.js
- * -> src/polyfills/array-includes.js.) This sequence changes rarely, so we can
- * use it as a sentinel value. Here is the process:
+ * src/polyfills/array-includes.js. (The import chain is src/amp.js ->
+ * src/polyfills/index.js -> src/polyfills/array-includes.js.) This sequence
+ * changes rarely, so we can use it as a sentinel value. Here is the process:
  *
  * 1. Decode the 'mappings' field into a 3d array using 'sourcemap-codec'.
  * 2. Extract the mapping for the first line of code in minified v0.js.
diff --git a/build-system/test-configs/dep-check-config.js b/build-system/test-configs/dep-check-config.js
index 513ee7880541..66ffd427fc08 100644
--- a/build-system/test-configs/dep-check-config.js
+++ b/build-system/test-configs/dep-check-config.js
@@ -434,30 +434,6 @@ exports.rules = [
     filesMatching: 'extensions/**/*.js',
     mustNotDependOn: 'src/base-element.js',
   },
-  {
-    filesMatching: 'src/polyfills/*.js',
-    mustNotDependOn: '**/*.js',
-    allowlist: [
-      'src/polyfills/fetch.js->src/log.js',
-      'src/polyfills/fetch.js->src/json.js',
-      'src/polyfills/fetch.js->src/core/types/index.js',
-      'src/polyfills/fetch.js->src/core/types/object.js',
-      'src/polyfills/fetch.js->src/utils/bytes.js',
-      'src/polyfills/intersection-observer.js->src/polyfills/stubs/intersection-observer-stub.js',
-      'src/polyfills/resize-observer.js->src/polyfills/stubs/resize-observer-stub.js',
-      'src/polyfills/custom-elements.js->src/core/data-structures/promise.js',
-    ],
-  },
-  {
-    filesMatching: 'src/polyfills/stubs/**/*.js',
-    mustNotDependOn: '**/*.js',
-    allowlist: [
-      'src/polyfills/stubs/intersection-observer-stub.js->src/services.js',
-      'src/polyfills/stubs/intersection-observer-stub.js->src/core/data-structures/promise.js',
-      'src/polyfills/stubs/resize-observer-stub.js->src/services.js',
-      'src/polyfills/stubs/resize-observer-stub.js->src/core/data-structures/promise.js',
-    ],
-  },
   {
     filesMatching: '**/*.js',
     mustNotDependOn: 'src/polyfills/*.js',
@@ -468,22 +444,24 @@ exports.rules = [
       '3p/polyfills.js->src/polyfills/object-values.js',
       '3p/polyfills.js->src/polyfills/promise.js',
       '3p/polyfills.js->src/polyfills/string-starts-with.js',
-      'src/polyfills.js->src/polyfills/abort-controller.js',
-      'src/polyfills.js->src/polyfills/domtokenlist.js',
-      'src/polyfills.js->src/polyfills/document-contains.js',
-      'src/polyfills.js->src/polyfills/fetch.js',
-      'src/polyfills.js->src/polyfills/math-sign.js',
-      'src/polyfills.js->src/polyfills/object-assign.js',
-      'src/polyfills.js->src/polyfills/object-values.js',
-      'src/polyfills.js->src/polyfills/promise.js',
-      'src/polyfills.js->src/polyfills/array-includes.js',
-      'src/polyfills.js->src/polyfills/string-starts-with.js',
-      'src/polyfills.js->src/polyfills/custom-elements.js',
-      'src/polyfills.js->src/polyfills/intersection-observer.js',
-      'src/polyfills.js->src/polyfills/resize-observer.js',
-      'src/polyfills.js->src/polyfills/map-set.js',
-      'src/polyfills.js->src/polyfills/set-add.js',
-      'src/polyfills.js->src/polyfills/weakmap-set.js',
+      'src/amp.js->src/polyfills/index.js',
+      'src/polyfills/index.js->src/polyfills/abort-controller.js',
+      'src/polyfills/index.js->src/polyfills/domtokenlist.js',
+      'src/polyfills/index.js->src/polyfills/document-contains.js',
+      'src/polyfills/index.js->src/polyfills/fetch.js',
+      'src/polyfills/index.js->src/polyfills/get-bounding-client-rect.js',
+      'src/polyfills/index.js->src/polyfills/math-sign.js',
+      'src/polyfills/index.js->src/polyfills/object-assign.js',
+      'src/polyfills/index.js->src/polyfills/object-values.js',
+      'src/polyfills/index.js->src/polyfills/promise.js',
+      'src/polyfills/index.js->src/polyfills/array-includes.js',
+      'src/polyfills/index.js->src/polyfills/string-starts-with.js',
+      'src/polyfills/index.js->src/polyfills/custom-elements.js',
+      'src/polyfills/index.js->src/polyfills/intersection-observer.js',
+      'src/polyfills/index.js->src/polyfills/resize-observer.js',
+      'src/polyfills/index.js->src/polyfills/map-set.js',
+      'src/polyfills/index.js->src/polyfills/set-add.js',
+      'src/polyfills/index.js->src/polyfills/weakmap-set.js',
       'src/friendly-iframe-embed.js->src/polyfills/abort-controller.js',
       'src/friendly-iframe-embed.js->src/polyfills/custom-elements.js',
       'src/friendly-iframe-embed.js->src/polyfills/document-contains.js',
@@ -494,8 +472,8 @@ exports.rules = [
   },
   {
     filesMatching: '**/*.js',
-    mustNotDependOn: 'src/polyfills.js',
-    allowlist: ['src/amp.js->src/polyfills.js'],
+    mustNotDependOn: 'src/polyfills/index.js',
+    allowlist: ['src/amp.js->src/polyfills/index.js'],
   },
 
   // Rules for main src.
diff --git a/build-system/test-configs/forbidden-terms.js b/build-system/test-configs/forbidden-terms.js
index 523554b5e4ad..760d1ba661d2 100644
--- a/build-system/test-configs/forbidden-terms.js
+++ b/build-system/test-configs/forbidden-terms.js
@@ -949,8 +949,7 @@ const forbiddenTermsSrcInclusive = {
     message: bannedTermsHelpString,
     allowlist: [
       'src/friendly-iframe-embed.js',
-      'src/polyfills/stubs/intersection-observer-stub.js',
-      'src/polyfills/stubs/resize-observer-stub.js',
+      'src/runtime.js',
       'src/service/extensions-impl.js',
       'src/service/crypto-impl.js',
     ],
diff --git a/extensions/amp-access/0.1/iframe-api/rollup.config.js b/extensions/amp-access/0.1/iframe-api/rollup.config.js
index b24997ba2ef4..4e8f618f7197 100644
--- a/extensions/amp-access/0.1/iframe-api/rollup.config.js
+++ b/extensions/amp-access/0.1/iframe-api/rollup.config.js
@@ -33,5 +33,5 @@ export default {
     }),
     cleanup(),
   ],
-  external: [path.resolve('../../../../src/polyfills.js')],
+  external: [path.resolve('../../../../src/polyfills/index.js')],
 };
diff --git a/src/.eslintrc.js b/src/.eslintrc.js
index 0f226b8aafe0..e9e92d11580d 100644
--- a/src/.eslintrc.js
+++ b/src/.eslintrc.js
@@ -42,6 +42,12 @@ module.exports = {
             'from': 'src',
             'except': ['./core', './context'],
           },
+          {
+            // Disallow importing non-core dependencies into polyfills
+            'target': 'src/polyfills',
+            'from': 'src',
+            'except': ['./core', './polyfills'],
+          },
         ],
       },
     ],
@@ -54,6 +60,8 @@ module.exports = {
         './preact/base-element.js',
         './preact/slot.js',
         './context/node.js',
+        './polyfills/fetch.js',
+        './polyfills/get-bounding-client-rect.js',
         // TEMPORARY, follow tracking issue #33631
         './preact/component/3p-frame.js',
       ],
diff --git a/src/get-bounding-client-rect.js b/src/polyfills/get-bounding-client-rect.js
similarity index 95%
rename from src/get-bounding-client-rect.js
rename to src/polyfills/get-bounding-client-rect.js
index cbbd1c20c132..e26115024752 100644
--- a/src/get-bounding-client-rect.js
+++ b/src/polyfills/get-bounding-client-rect.js
@@ -21,8 +21,8 @@
  * @see https://developer.microsoft.com/en-us/microsoft-edge/platform/issues/106812/
  */
 
-import {LayoutRectDef, layoutRectLtwh} from './layout-rect';
-import {isConnectedNode} from './dom';
+import {LayoutRectDef, layoutRectLtwh} from '../layout-rect';
+import {isConnectedNode} from '../dom';
 
 /**
  * Stores the native getBoundingClientRect before we patch it, so that the
diff --git a/src/polyfills.js b/src/polyfills/index.js
similarity index 55%
rename from src/polyfills.js
rename to src/polyfills/index.js
index 60f50edd4b1f..e903bac80204 100644
--- a/src/polyfills.js
+++ b/src/polyfills/index.js
@@ -14,25 +14,25 @@
  * limitations under the License.
  */
 
-/** @fileoverview */
+/** @fileoverview Installs polyfills depending on build environment. */
 
-import {install as installAbortController} from './polyfills/abort-controller';
-import {install as installArrayIncludes} from './polyfills/array-includes';
-import {install as installCustomElements} from './polyfills/custom-elements';
-import {install as installDOMTokenList} from './polyfills/domtokenlist';
-import {install as installDocContains} from './polyfills/document-contains';
-import {install as installFetch} from './polyfills/fetch';
+import {install as installAbortController} from './abort-controller';
+import {install as installArrayIncludes} from './array-includes';
+import {install as installCustomElements} from './custom-elements';
+import {install as installDOMTokenList} from './domtokenlist';
+import {install as installDocContains} from './document-contains';
+import {install as installFetch} from './fetch';
 import {install as installGetBoundingClientRect} from './get-bounding-client-rect';
-import {install as installIntersectionObserver} from './polyfills/intersection-observer';
-import {install as installMapSet} from './polyfills/map-set';
-import {install as installMathSign} from './polyfills/math-sign';
-import {install as installObjectAssign} from './polyfills/object-assign';
-import {install as installObjectValues} from './polyfills/object-values';
-import {install as installPromise} from './polyfills/promise';
-import {install as installResizeObserver} from './polyfills/resize-observer';
-import {install as installSetAdd} from './polyfills/set-add';
-import {install as installStringStartsWith} from './polyfills/string-starts-with';
-import {install as installWeakMapSet} from './polyfills/weakmap-set';
+import {install as installIntersectionObserver} from './intersection-observer';
+import {install as installMapSet} from './map-set';
+import {install as installMathSign} from './math-sign';
+import {install as installObjectAssign} from './object-assign';
+import {install as installObjectValues} from './object-values';
+import {install as installPromise} from './promise';
+import {install as installResizeObserver} from './resize-observer';
+import {install as installSetAdd} from './set-add';
+import {install as installStringStartsWith} from './string-starts-with';
+import {install as installWeakMapSet} from './weakmap-set';
 
 if (!IS_ESM) {
   installFetch(self);
diff --git a/src/polyfills/intersection-observer.js b/src/polyfills/intersection-observer.js
index 431ab69de319..6268ac8b0c8e 100644
--- a/src/polyfills/intersection-observer.js
+++ b/src/polyfills/intersection-observer.js
@@ -22,7 +22,7 @@
 import {
   installStub,
   shouldLoadPolyfill,
-} from '../polyfills/stubs/intersection-observer-stub';
+} from './stubs/intersection-observer-stub';
 
 /**
  * Installs the IntersectionObserver polyfill. There are a few different modes of operation.
diff --git a/src/polyfills/resize-observer.js b/src/polyfills/resize-observer.js
index 02a78998ff8e..795b68b9b534 100644
--- a/src/polyfills/resize-observer.js
+++ b/src/polyfills/resize-observer.js
@@ -19,10 +19,7 @@
  * See https://developer.mozilla.org/en-US/docs/Web/API/ResizeObserver
  */
 
-import {
-  installStub,
-  shouldLoadPolyfill,
-} from '../polyfills/stubs/resize-observer-stub';
+import {installStub, shouldLoadPolyfill} from './stubs/resize-observer-stub';
 
 /**
  * Installs the ResizeObserver polyfill. There are a few different modes of
diff --git a/src/polyfills/stubs/intersection-observer-stub.js b/src/polyfills/stubs/intersection-observer-stub.js
index 480ab580437c..baca8160e620 100644
--- a/src/polyfills/stubs/intersection-observer-stub.js
+++ b/src/polyfills/stubs/intersection-observer-stub.js
@@ -23,8 +23,6 @@
  * amp-intersection-observer-polyfill extension.
  */
 
-import {Services} from '../../services';
-
 const UPGRADERS = '_upgraders';
 const NATIVE = '_native';
 const STUB = '_stub';
@@ -110,17 +108,6 @@ export function supportsDocumentRoot(win) {
   }
 }
 
-/**
- * @param {!Window} win
- */
-export function scheduleUpgradeIfNeeded(win) {
-  if (shouldLoadPolyfill(win)) {
-    Services.extensionsFor(win).preloadExtension(
-      'amp-intersection-observer-polyfill'
-    );
-  }
-}
-
 /**
  * @param {!Window} win
  * @param {function()} installer
diff --git a/src/polyfills/stubs/resize-observer-stub.js b/src/polyfills/stubs/resize-observer-stub.js
index b18289ddcfbe..d7631ad091d3 100644
--- a/src/polyfills/stubs/resize-observer-stub.js
+++ b/src/polyfills/stubs/resize-observer-stub.js
@@ -23,8 +23,6 @@
  * amp-resize-observer-polyfill extension.
  */
 
-import {Services} from '../../services';
-
 const UPGRADERS = '_upgraders';
 const STUB = '_stub';
 
@@ -51,17 +49,6 @@ export function installStub(win) {
   win.ResizeObserver[STUB] = ResizeObserverStub;
 }
 
-/**
- * @param {!Window} win
- */
-export function scheduleUpgradeIfNeeded(win) {
-  if (shouldLoadPolyfill(win)) {
-    Services.extensionsFor(win).preloadExtension(
-      'amp-resize-observer-polyfill'
-    );
-  }
-}
-
 /**
  * @param {!Window} win
  * @param {function()} installer
diff --git a/src/runtime.js b/src/runtime.js
index 0a93e2640d18..7da2ca1d4bc1 100644
--- a/src/runtime.js
+++ b/src/runtime.js
@@ -40,9 +40,9 @@ import {
 import {internalRuntimeVersion} from './internal-version';
 import {isExperimentOn, toggleExperiment} from './experiments';
 import {reportErrorForWin} from './error-reporting';
-import {scheduleUpgradeIfNeeded as scheduleInObUpgradeIfNeeded} from './polyfills/stubs/intersection-observer-stub';
-import {scheduleUpgradeIfNeeded as scheduleResObUpgradeIfNeeded} from './polyfills/stubs/resize-observer-stub';
 import {setStyle} from './style';
+import {shouldLoadPolyfill as shouldLoadInObPolyfill} from './polyfills/stubs/intersection-observer-stub';
+import {shouldLoadPolyfill as shouldLoadResObPolyfill} from './polyfills/stubs/resize-observer-stub';
 import {startupChunk} from './chunk';
 import {stubElementsForDoc} from './service/custom-element-registry';
 import {waitForBodyOpenPromise} from './dom';
@@ -262,8 +262,13 @@ function adoptShared(global, callback) {
   }
 
   // Some deferred polyfills.
-  scheduleInObUpgradeIfNeeded(global);
-  scheduleResObUpgradeIfNeeded(global);
+  const extensionsFor = Services.extensionsFor(global);
+  if (shouldLoadResObPolyfill(global)) {
+    extensionsFor.preloadExtension('amp-resize-observer-polyfill');
+  }
+  if (shouldLoadInObPolyfill(global)) {
+    extensionsFor.preloadExtension('amp-intersection-observer-polyfill');
+  }
 
   return iniPromise;
 }