diff --git a/fixtures/fizz-ssr-browser/index.html b/fixtures/fizz-ssr-browser/index.html
index fa79435067..6320c4a56b 100644
--- a/fixtures/fizz-ssr-browser/index.html
+++ b/fixtures/fizz-ssr-browser/index.html
@@ -21,9 +21,14 @@
     <script src="https://unpkg.com/babel-standalone@6/babel.js"></script>
     <script type="text/babel">
       let controller = new AbortController();
-      let stream = ReactDOMFizzServer.renderToReadableStream(<body>Success</body>, {
-        signal: controller.signal,
-      });
+      let stream = ReactDOMFizzServer.renderToReadableStream(
+        <html>
+          <body>Success</body>
+        </html>,
+        {
+          signal: controller.signal,
+        }
+      );
       let response = new Response(stream, {
         headers: {'Content-Type': 'text/html'},
       });
diff --git a/fixtures/ssr/server/render.js b/fixtures/ssr/server/render.js
index 5a37f5c555..ae441545d8 100644
--- a/fixtures/ssr/server/render.js
+++ b/fixtures/ssr/server/render.js
@@ -28,8 +28,6 @@ export default function render(url, res) {
         // If something errored before we started streaming, we set the error code appropriately.
         res.statusCode = didError ? 500 : 200;
         res.setHeader('Content-type', 'text/html');
-        // There's no way to render a doctype in React so prepend manually.
-        res.write('<!DOCTYPE html>');
         startWriting();
       },
       onError(x) {
diff --git a/packages/react-dom/src/__tests__/ReactDOMFizzServerBrowser-test.js b/packages/react-dom/src/__tests__/ReactDOMFizzServerBrowser-test.js
index c813b6f558..fd256f1a55 100644
--- a/packages/react-dom/src/__tests__/ReactDOMFizzServerBrowser-test.js
+++ b/packages/react-dom/src/__tests__/ReactDOMFizzServerBrowser-test.js
@@ -58,6 +58,19 @@ describe('ReactDOMFizzServer', () => {
     expect(result).toMatchInlineSnapshot(`"<div>hello world</div>"`);
   });
 
+  // @gate experimental
+  it('should emit DOCTYPE at the root of the document', async () => {
+    const stream = ReactDOMFizzServer.renderToReadableStream(
+      <html>
+        <body>hello world</body>
+      </html>,
+    );
+    const result = await readResult(stream);
+    expect(result).toMatchInlineSnapshot(
+      `"<!DOCTYPE html><html><body>hello world</body></html>"`,
+    );
+  });
+
   // @gate experimental
   it('emits all HTML as one unit if we wait until the end to start', async () => {
     let hasLoaded = false;
diff --git a/packages/react-dom/src/__tests__/ReactDOMFizzServerNode-test.js b/packages/react-dom/src/__tests__/ReactDOMFizzServerNode-test.js
index 7afc45aa4a..be0b665ea6 100644
--- a/packages/react-dom/src/__tests__/ReactDOMFizzServerNode-test.js
+++ b/packages/react-dom/src/__tests__/ReactDOMFizzServerNode-test.js
@@ -68,6 +68,22 @@ describe('ReactDOMFizzServer', () => {
     expect(output.result).toMatchInlineSnapshot(`"<div>hello world</div>"`);
   });
 
+  // @gate experimental
+  it('should emit DOCTYPE at the root of the document', () => {
+    const {writable, output} = getTestWritable();
+    const {startWriting} = ReactDOMFizzServer.pipeToNodeWritable(
+      <html>
+        <body>hello world</body>
+      </html>,
+      writable,
+    );
+    startWriting();
+    jest.runAllTimers();
+    expect(output.result).toMatchInlineSnapshot(
+      `"<!DOCTYPE html><html><body>hello world</body></html>"`,
+    );
+  });
+
   // @gate experimental
   it('should start writing after startWriting', () => {
     const {writable, output} = getTestWritable();
diff --git a/packages/react-dom/src/__tests__/ReactRenderDocument-test.js b/packages/react-dom/src/__tests__/ReactRenderDocument-test.js
index 8003ee06cb..95b814b331 100644
--- a/packages/react-dom/src/__tests__/ReactRenderDocument-test.js
+++ b/packages/react-dom/src/__tests__/ReactRenderDocument-test.js
@@ -49,6 +49,7 @@ describe('rendering React components at document', () => {
       }
 
       const markup = ReactDOMServer.renderToString(<Root hello="world" />);
+      expect(markup).not.toContain('DOCTYPE');
       const testDocument = getTestDocument(markup);
       const body = testDocument.body;
 
diff --git a/packages/react-dom/src/server/ReactDOMLegacyServerBrowser.js b/packages/react-dom/src/server/ReactDOMLegacyServerBrowser.js
index 4f0d619417..991c83e32e 100644
--- a/packages/react-dom/src/server/ReactDOMLegacyServerBrowser.js
+++ b/packages/react-dom/src/server/ReactDOMLegacyServerBrowser.js
@@ -64,7 +64,7 @@ function renderToStringImpl(
       generateStaticMarkup,
       options ? options.identifierPrefix : undefined,
     ),
-    createRootFormatContext(undefined),
+    createRootFormatContext(),
     Infinity,
     onError,
     undefined,
diff --git a/packages/react-dom/src/server/ReactDOMLegacyServerNode.js b/packages/react-dom/src/server/ReactDOMLegacyServerNode.js
index bc1e132209..ce2924c9a5 100644
--- a/packages/react-dom/src/server/ReactDOMLegacyServerNode.js
+++ b/packages/react-dom/src/server/ReactDOMLegacyServerNode.js
@@ -79,7 +79,7 @@ function renderToNodeStreamImpl(
     children,
     destination,
     createResponseState(false, options ? options.identifierPrefix : undefined),
-    createRootFormatContext(undefined),
+    createRootFormatContext(),
     Infinity,
     onError,
     onCompleteAll,
diff --git a/packages/react-dom/src/server/ReactDOMServerFormatConfig.js b/packages/react-dom/src/server/ReactDOMServerFormatConfig.js
index 6dfa245ae4..9232106aac 100644
--- a/packages/react-dom/src/server/ReactDOMServerFormatConfig.js
+++ b/packages/react-dom/src/server/ReactDOMServerFormatConfig.js
@@ -87,9 +87,10 @@ export function createResponseState(
 // Constants for the insertion mode we're currently writing in. We don't encode all HTML5 insertion
 // modes. We only include the variants as they matter for the sake of our purposes.
 // We don't actually provide the namespace therefore we use constants instead of the string.
-const HTML_MODE = 0;
-const SVG_MODE = 1;
-const MATHML_MODE = 2;
+const ROOT_HTML_MODE = 0; // Used for the root most element tag.
+export const HTML_MODE = 1;
+const SVG_MODE = 2;
+const MATHML_MODE = 3;
 const HTML_TABLE_MODE = 4;
 const HTML_TABLE_BODY_MODE = 5;
 const HTML_TABLE_ROW_MODE = 6;
@@ -121,7 +122,7 @@ export function createRootFormatContext(namespaceURI?: string): FormatContext {
       ? SVG_MODE
       : namespaceURI === 'http://www.w3.org/1998/Math/MathML'
       ? MATHML_MODE
-      : HTML_MODE;
+      : ROOT_HTML_MODE;
   return createFormatContext(insertionMode, null);
 }
 
@@ -160,6 +161,10 @@ export function getChildFormatContext(
     // entered plain HTML again.
     return createFormatContext(HTML_MODE, null);
   }
+  if (parentContext.insertionMode === ROOT_HTML_MODE) {
+    // We've emitted the root and is now in plain HTML mode.
+    return createFormatContext(HTML_MODE, null);
+  }
   return parentContext;
 }
 
@@ -1262,6 +1267,8 @@ function startChunkForTag(tag: string): PrecomputedChunk {
   return tagStartChunk;
 }
 
+const DOCTYPE: PrecomputedChunk = stringToPrecomputedChunk('<!DOCTYPE html>');
+
 export function pushStartInstance(
   target: Array<Chunk | PrecomputedChunk>,
   type: string,
@@ -1371,6 +1378,21 @@ export function pushStartInstance(
         assignID,
       );
     }
+    case 'html': {
+      if (formatContext.insertionMode === ROOT_HTML_MODE) {
+        // If we're rendering the html tag and we're at the root (i.e. not in foreignObject)
+        // then we also emit the DOCTYPE as part of the root content as a convenience for
+        // rendering the whole document.
+        target.push(DOCTYPE);
+      }
+      return pushStartGenericElement(
+        target,
+        props,
+        type,
+        responseState,
+        assignID,
+      );
+    }
     default: {
       if (type.indexOf('-') === -1 && typeof props.is !== 'string') {
         // Generic element
@@ -1541,6 +1563,7 @@ export function writeStartSegment(
   id: number,
 ): boolean {
   switch (formatContext.insertionMode) {
+    case ROOT_HTML_MODE:
     case HTML_MODE: {
       writeChunk(destination, startSegmentHTML);
       writeChunk(destination, responseState.segmentPrefix);
@@ -1597,6 +1620,7 @@ export function writeEndSegment(
   formatContext: FormatContext,
 ): boolean {
   switch (formatContext.insertionMode) {
+    case ROOT_HTML_MODE:
     case HTML_MODE: {
       return writeChunk(destination, endSegmentHTML);
     }
diff --git a/packages/react-dom/src/server/ReactDOMServerLegacyFormatConfig.js b/packages/react-dom/src/server/ReactDOMServerLegacyFormatConfig.js
index dbca4b43ab..3dc354b452 100644
--- a/packages/react-dom/src/server/ReactDOMServerLegacyFormatConfig.js
+++ b/packages/react-dom/src/server/ReactDOMServerLegacyFormatConfig.js
@@ -7,7 +7,10 @@
  * @flow
  */
 
-import type {SuspenseBoundaryID} from './ReactDOMServerFormatConfig';
+import type {
+  SuspenseBoundaryID,
+  FormatContext,
+} from './ReactDOMServerFormatConfig';
 
 import {
   createResponseState as createResponseStateImpl,
@@ -16,6 +19,7 @@ import {
   writeStartClientRenderedSuspenseBoundary as writeStartClientRenderedSuspenseBoundaryImpl,
   writeEndCompletedSuspenseBoundary as writeEndCompletedSuspenseBoundaryImpl,
   writeEndClientRenderedSuspenseBoundary as writeEndClientRenderedSuspenseBoundaryImpl,
+  HTML_MODE,
 } from './ReactDOMServerFormatConfig';
 
 import type {
@@ -62,6 +66,13 @@ export function createResponseState(
   };
 }
 
+export function createRootFormatContext(): FormatContext {
+  return {
+    insertionMode: HTML_MODE, // We skip the root mode because we don't want to emit the DOCTYPE in legacy mode.
+    selectedValue: null,
+  };
+}
+
 export type {
   FormatContext,
   SuspenseBoundaryID,
@@ -69,7 +80,6 @@ export type {
 } from './ReactDOMServerFormatConfig';
 
 export {
-  createRootFormatContext,
   getChildFormatContext,
   createSuspenseBoundaryID,
   makeServerID,
