diff --git a/_locales/en/messages.json b/_locales/en/messages.json
index 1ab98801c5..6813abf4d3 100644
--- a/_locales/en/messages.json
+++ b/_locales/en/messages.json
@@ -2711,6 +2711,10 @@
     "message": "Cancel",
     "description": "Appears on the cancel button in confirmation dialogs."
   },
+  "MessageBody--read-more": {
+    "message": "Read more",
+    "description": "When a message is too long this is the affordance to expand the message"
+  },
   "Message--unsupported-message": {
     "message": "$contact$ sent you a message that can't be processed or displayed because it uses a new Signal feature.",
     "placeholders": {
diff --git a/stylesheets/_modules.scss b/stylesheets/_modules.scss
index 5242981f7a..f33a4cd9e6 100644
--- a/stylesheets/_modules.scss
+++ b/stylesheets/_modules.scss
@@ -4518,48 +4518,6 @@ button.module-image__border-overlay:focus {
   background-color: $color-white;
 }
 
-// Module: Highlighted Message Body
-
-.module-message-body__highlight {
-  font-weight: bold;
-}
-
-.module-message-body__at-mention {
-  border-radius: 4px;
-  cursor: pointer;
-  display: inline-block;
-  padding-left: 4px;
-  padding-right: 4px;
-  border: 1px solid transparent;
-
-  @include light-theme {
-    background-color: $color-gray-20;
-  }
-
-  @include dark-theme {
-    background-color: $color-black-alpha-40;
-  }
-
-  &:focus {
-    border: 1px solid $color-black;
-    outline: none;
-  }
-}
-
-.module-message-body__at-mention--incoming {
-  @include light-theme {
-    background-color: $color-gray-20;
-  }
-
-  @include dark-theme {
-    background-color: $color-gray-60;
-  }
-}
-
-.module-message-body__at-mention--outgoing {
-  background-color: $color-black-alpha-40;
-}
-
 // Module: Reaction Viewer
 
 .module-reaction-viewer {
diff --git a/stylesheets/components/MessageBody.scss b/stylesheets/components/MessageBody.scss
new file mode 100644
index 0000000000..74435d8622
--- /dev/null
+++ b/stylesheets/components/MessageBody.scss
@@ -0,0 +1,53 @@
+// Copyright 2021 Signal Messenger, LLC
+// SPDX-License-Identifier: AGPL-3.0-only
+
+.MessageBody {
+  &__highlight {
+    font-weight: bold;
+  }
+
+  &__read-more {
+    @include button-reset;
+    font-weight: bold;
+
+    &:focus {
+      color: $color-ultramarine;
+    }
+  }
+
+  &__at-mention {
+    border-radius: 4px;
+    cursor: pointer;
+    display: inline-block;
+    padding-left: 4px;
+    padding-right: 4px;
+    border: 1px solid transparent;
+
+    @include light-theme {
+      background-color: $color-gray-20;
+    }
+
+    @include dark-theme {
+      background-color: $color-black-alpha-40;
+    }
+
+    &:focus {
+      border: 1px solid $color-black;
+      outline: none;
+    }
+
+    &--incoming {
+      @include light-theme {
+        background-color: $color-gray-20;
+      }
+
+      @include dark-theme {
+        background-color: $color-gray-60;
+      }
+    }
+
+    &--outgoing {
+      background-color: $color-black-alpha-40;
+    }
+  }
+}
diff --git a/stylesheets/manifest.scss b/stylesheets/manifest.scss
index b8e8ea13d7..9f4013c93f 100644
--- a/stylesheets/manifest.scss
+++ b/stylesheets/manifest.scss
@@ -68,6 +68,7 @@
 @import './components/Lightbox.scss';
 @import './components/MediaQualitySelector.scss';
 @import './components/MessageAudio.scss';
+@import './components/MessageBody.scss';
 @import './components/MessageDetail.scss';
 @import './components/Modal.scss';
 @import './components/PermissionsPopup.scss';
diff --git a/ts/components/conversation/AtMentionify.tsx b/ts/components/conversation/AtMentionify.tsx
index 3c3726bbb4..877d0074b9 100644
--- a/ts/components/conversation/AtMentionify.tsx
+++ b/ts/components/conversation/AtMentionify.tsx
@@ -46,7 +46,7 @@ export const AtMentionify = ({
     if (range) {
       results.push(
         <span
-          className={`module-message-body__at-mention module-message-body__at-mention--${direction}`}
+          className={`MessageBody__at-mention MessageBody__at-mention--${direction}`}
           key={range.start}
           onClick={() => {
             if (openConversation && range.conversationID) {
diff --git a/ts/components/conversation/Message.tsx b/ts/components/conversation/Message.tsx
index 3f17781b24..9dd2299d3f 100644
--- a/ts/components/conversation/Message.tsx
+++ b/ts/components/conversation/Message.tsx
@@ -17,7 +17,7 @@ import {
 import { ReadStatus } from '../../messages/MessageReadStatus';
 import { Avatar } from '../Avatar';
 import { Spinner } from '../Spinner';
-import { MessageBody } from './MessageBody';
+import { MessageBodyReadMore } from './MessageBodyReadMore';
 import { MessageMetadata } from './MessageMetadata';
 import { ImageGrid } from './ImageGrid';
 import { GIF } from './GIF';
@@ -1224,6 +1224,7 @@ export class Message extends React.PureComponent<Props, State> {
       deletedForEveryone,
       direction,
       i18n,
+      onHeightChange,
       openConversation,
       status,
       text,
@@ -1252,12 +1253,13 @@ export class Message extends React.PureComponent<Props, State> {
             : null
         )}
       >
-        <MessageBody
+        <MessageBodyReadMore
           bodyRanges={bodyRanges}
           disableLinks={!this.areLinksEnabled()}
           direction={direction}
           i18n={i18n}
           openConversation={openConversation}
+          onHeightChange={onHeightChange}
           text={contents || ''}
           textPending={textPending}
         />
diff --git a/ts/components/conversation/MessageBody.tsx b/ts/components/conversation/MessageBody.tsx
index 47bca72826..db24ba65ec 100644
--- a/ts/components/conversation/MessageBody.tsx
+++ b/ts/components/conversation/MessageBody.tsx
@@ -1,7 +1,7 @@
-// Copyright 2018-2020 Signal Messenger, LLC
+// Copyright 2018-2021 Signal Messenger, LLC
 // SPDX-License-Identifier: AGPL-3.0-only
 
-import React from 'react';
+import React, { KeyboardEvent } from 'react';
 
 import { getSizeClass, SizeClassType } from '../emoji/lib';
 import { AtMentionify } from './AtMentionify';
@@ -30,6 +30,7 @@ export type Props = {
   disableLinks?: boolean;
   i18n: LocalizerType;
   bodyRanges?: BodyRangesType;
+  onIncreaseTextLength?: () => unknown;
   openConversation?: OpenConversationActionType;
 };
 
@@ -59,21 +60,39 @@ const renderEmoji = ({
  * configurable with their `renderXXX` props, this component will assemble all three of
  * them for you.
  */
-export class MessageBody extends React.Component<Props> {
-  private readonly renderNewLines: RenderTextCallbackType = ({
+export function MessageBody({
+  bodyRanges,
+  direction,
+  disableJumbomoji,
+  disableLinks,
+  i18n,
+  onIncreaseTextLength,
+  openConversation,
+  text,
+  textPending,
+}: Props): JSX.Element {
+  const hasReadMore = Boolean(onIncreaseTextLength);
+  const textWithSuffix = textPending || hasReadMore ? `${text}...` : text;
+
+  const sizeClass = disableJumbomoji ? undefined : getSizeClass(text);
+  const processedText = AtMentionify.preprocessMentions(
+    textWithSuffix,
+    bodyRanges
+  );
+
+  const renderNewLines: RenderTextCallbackType = ({
     text: textWithNewLines,
     key,
   }) => {
-    const { bodyRanges, direction, openConversation } = this.props;
     return (
       <AddNewLines
         key={key}
         text={textWithNewLines}
-        renderNonNewLine={({ text, key: innerKey }) => (
+        renderNonNewLine={({ text: innerText, key: innerKey }) => (
           <AtMentionify
             key={innerKey}
             direction={direction}
-            text={text}
+            text={innerText}
             bodyRanges={bodyRanges}
             openConversation={openConversation}
           />
@@ -82,62 +101,51 @@ export class MessageBody extends React.Component<Props> {
     );
   };
 
-  public addDownloading(jsx: JSX.Element): JSX.Element {
-    const { i18n, textPending } = this.props;
-
-    return (
-      <span>
-        {jsx}
-        {textPending ? (
-          <span className="module-message-body__highlight">
-            {' '}
-            {i18n('downloading')}
-          </span>
-        ) : null}
-      </span>
-    );
-  }
-
-  public render(): JSX.Element {
-    const {
-      bodyRanges,
-      text,
-      textPending,
-      disableJumbomoji,
-      disableLinks,
-      i18n,
-    } = this.props;
-    const sizeClass = disableJumbomoji ? undefined : getSizeClass(text);
-    const textWithPending = AtMentionify.preprocessMentions(
-      textPending ? `${text}...` : text,
-      bodyRanges
-    );
-
-    if (disableLinks) {
-      return this.addDownloading(
+  return (
+    <span>
+      {disableLinks ? (
         renderEmoji({
           i18n,
-          text: textWithPending,
+          text: processedText,
           sizeClass,
           key: 0,
-          renderNonEmoji: this.renderNewLines,
+          renderNonEmoji: renderNewLines,
         })
-      );
-    }
-
-    return this.addDownloading(
-      <Linkify
-        text={textWithPending}
-        renderNonLink={({ key, text: nonLinkText }) => {
-          return renderEmoji({
-            i18n,
-            text: nonLinkText,
-            sizeClass,
-            key,
-            renderNonEmoji: this.renderNewLines,
-          });
-        }}
-      />
-    );
-  }
+      ) : (
+        <Linkify
+          text={processedText}
+          renderNonLink={({ key, text: nonLinkText }) => {
+            return renderEmoji({
+              i18n,
+              text: nonLinkText,
+              sizeClass,
+              key,
+              renderNonEmoji: renderNewLines,
+            });
+          }}
+        />
+      )}
+      {textPending ? (
+        <span className="MessageBody__highlight"> {i18n('downloading')}</span>
+      ) : null}
+      {onIncreaseTextLength ? (
+        <button
+          className="MessageBody__read-more"
+          onClick={() => {
+            onIncreaseTextLength();
+          }}
+          onKeyDown={(ev: KeyboardEvent) => {
+            if (ev.key === 'Space' || ev.key === 'Enter') {
+              onIncreaseTextLength();
+            }
+          }}
+          tabIndex={0}
+          type="button"
+        >
+          {' '}
+          {i18n('MessageBody--read-more')}
+        </button>
+      ) : null}
+    </span>
+  );
 }
diff --git a/ts/components/conversation/MessageBodyReadMore.stories.tsx b/ts/components/conversation/MessageBodyReadMore.stories.tsx
new file mode 100644
index 0000000000..c378ea7ba2
--- /dev/null
+++ b/ts/components/conversation/MessageBodyReadMore.stories.tsx
@@ -0,0 +1,153 @@
+// Copyright 2021 Signal Messenger, LLC
+// SPDX-License-Identifier: AGPL-3.0-only
+
+import React from 'react';
+
+import { action } from '@storybook/addon-actions';
+import { text } from '@storybook/addon-knobs';
+import { storiesOf } from '@storybook/react';
+
+import { MessageBodyReadMore, Props } from './MessageBodyReadMore';
+import { setupI18n } from '../../util/setupI18n';
+import enMessages from '../../../_locales/en/messages.json';
+
+const i18n = setupI18n('en', enMessages);
+
+const story = storiesOf('Components/Conversation/MessageBodyReadMore', module);
+
+const createProps = (overrideProps: Partial<Props> = {}): Props => ({
+  bodyRanges: overrideProps.bodyRanges,
+  direction: 'incoming',
+  i18n,
+  onHeightChange: action('onHeightChange'),
+  text: text('text', overrideProps.text || ''),
+});
+
+story.add('Lots of cake with a cherry on top', () => (
+  <MessageBodyReadMore
+    {...createProps({
+      text: `x${'🍰'.repeat(399)}🍒`,
+    })}
+  />
+));
+
+story.add('Cherry overflow', () => (
+  <MessageBodyReadMore
+    {...createProps({
+      text: `x${'🍰'.repeat(400)}🍒`,
+    })}
+  />
+));
+
+story.add('Excessive amounts of cake', () => (
+  <MessageBodyReadMore
+    {...createProps({
+      text: `x${'🍰'.repeat(20000)}`,
+    })}
+  />
+));
+
+story.add('Long text', () => (
+  <MessageBodyReadMore
+    {...createProps({
+      text: `
+      SCENE I. Rome. A street.
+      Enter FLAVIUS, MARULLUS, and certain Commoners
+      FLAVIUS
+      Hence! home, you idle creatures get you home:
+      Is this a holiday? what! know you not,
+      Being mechanical, you ought not walk
+      Upon a labouring day without the sign
+      Of your profession? Speak, what trade art thou?
+      First Commoner
+      Why, sir, a carpenter.
+      MARULLUS
+      Where is thy leather apron and thy rule?
+      What dost thou with thy best apparel on?
+      You, sir, what trade are you?
+      Second Commoner
+      Truly, sir, in respect of a fine workman, I am but,
+      as you would say, a cobbler.
+      MARULLUS
+      But what trade art thou? answer me directly.
+      Second Commoner
+      A trade, sir, that, I hope, I may use with a safe
+      conscience; which is, indeed, sir, a mender of bad soles.
+      MARULLUS
+      What trade, thou knave? thou naughty knave, what trade?
+      Second Commoner
+      Nay, I beseech you, sir, be not out with me: yet,
+      if you be out, sir, I can mend you.
+      MARULLUS
+      What meanest thou by that? mend me, thou saucy fellow!
+      Second Commoner
+      Why, sir, cobble you.
+      FLAVIUS
+      Thou art a cobbler, art thou?
+      Second Commoner
+      Truly, sir, all that I live by is with the awl: I
+      meddle with no tradesman's matters, nor women's
+      matters, but with awl. I am, indeed, sir, a surgeon
+      to old shoes; when they are in great danger, I
+      recover them. As proper men as ever trod upon
+      neat's leather have gone upon my handiwork.
+      FLAVIUS
+      But wherefore art not in thy shop today?
+      Why dost thou lead these men about the streets?
+      Second Commoner
+      Truly, sir, to wear out their shoes, to get myself
+      into more work. But, indeed, sir, we make holiday,
+      to see Caesar and to rejoice in his triumph.
+      MARULLUS
+      Wherefore rejoice? What conquest brings he home?
+      What tributaries follow him to Rome,
+      To grace in captive bonds his chariot-wheels?
+      You blocks, you stones, you worse than senseless things!
+      O you hard hearts, you cruel men of Rome,
+      Knew you not Pompey? Many a time and oft
+      Have you climb'd up to walls and battlements,
+      To towers and windows, yea, to chimney-tops,
+      Your infants in your arms, and there have sat
+      The livelong day, with patient expectation,
+      To see great Pompey pass the streets of Rome:
+      And when you saw his chariot but appear,
+      Have you not made an universal shout,
+      That Tiber trembled underneath her banks,
+      To hear the replication of your sounds
+      Made in her concave shores?
+      And do you now put on your best attire?
+      And do you now cull out a holiday?
+      And do you now strew flowers in his way
+      That comes in triumph over Pompey's blood? Be gone!
+      Run to your houses, fall upon your knees,
+      Pray to the gods to intermit the plague
+      That needs must light on this ingratitude.
+      FLAVIUS
+      Go, go, good countrymen, and, for this fault,
+      Assemble all the poor men of your sort;
+      Draw them to Tiber banks, and weep your tears
+      Into the channel, till the lowest stream
+      Do kiss the most exalted shores of all.
+      Exeunt all the Commoners
+      See whether their basest metal be not moved;
+      They vanish tongue-tied in their guiltiness.
+      Go you down that way towards the Capitol;
+      This way will I
+      disrobe the images,
+      If you do find them deck'd with ceremonies.
+      MARULLUS
+      May we do so?
+      You know it is the feast of Lupercal.
+      FLAVIUS
+      It is no matter; let no images
+      Be hung with Caesar's trophies. I'll about,
+      And drive away the vulgar from the streets:
+      So do you too, where you perceive them thick.
+      These growing feathers pluck'd from Caesar's wing
+      Will make him fly an ordinary pitch,
+      Who else would soar above the view of men
+      And keep us all in servile fearfulness.
+      `,
+    })}
+  />
+));
diff --git a/ts/components/conversation/MessageBodyReadMore.tsx b/ts/components/conversation/MessageBodyReadMore.tsx
new file mode 100644
index 0000000000..e6e7fa9929
--- /dev/null
+++ b/ts/components/conversation/MessageBodyReadMore.tsx
@@ -0,0 +1,88 @@
+// Copyright 2021 Signal Messenger, LLC
+// SPDX-License-Identifier: AGPL-3.0-only
+
+import React, { useState } from 'react';
+
+import { MessageBody, Props as MessageBodyPropsType } from './MessageBody';
+
+export type Props = Pick<
+  MessageBodyPropsType,
+  | 'direction'
+  | 'text'
+  | 'textPending'
+  | 'disableLinks'
+  | 'i18n'
+  | 'bodyRanges'
+  | 'openConversation'
+> & {
+  onHeightChange: () => unknown;
+};
+
+const INITIAL_LENGTH = 800;
+const INCREMENT_COUNT = 3000;
+
+function graphemeAwareSlice(
+  str: string,
+  length: number
+): {
+  hasReadMore: boolean;
+  text: string;
+} {
+  if (str.length <= length) {
+    return { text: str, hasReadMore: false };
+  }
+
+  let text: string | undefined;
+
+  for (const { index } of new Intl.Segmenter().segment(str)) {
+    if (!text && index >= length) {
+      text = str.slice(0, index);
+    }
+    if (text && index > length) {
+      return {
+        text,
+        hasReadMore: true,
+      };
+    }
+  }
+
+  return {
+    text: str,
+    hasReadMore: false,
+  };
+}
+
+export function MessageBodyReadMore({
+  bodyRanges,
+  direction,
+  disableLinks,
+  i18n,
+  onHeightChange,
+  openConversation,
+  text,
+  textPending,
+}: Props): JSX.Element {
+  const [maxLength, setMaxLength] = useState(INITIAL_LENGTH);
+
+  const { hasReadMore, text: slicedText } = graphemeAwareSlice(text, maxLength);
+
+  const onIncreaseTextLength = hasReadMore
+    ? () => {
+        setMaxLength(oldMaxLength => oldMaxLength + INCREMENT_COUNT);
+        onHeightChange();
+      }
+    : undefined;
+
+  return (
+    <MessageBody
+      bodyRanges={bodyRanges}
+      disableLinks={disableLinks}
+      direction={direction}
+      i18n={i18n}
+      onIncreaseTextLength={onIncreaseTextLength}
+      openConversation={openConversation}
+      text={slicedText}
+      textPending={textPending}
+    />
+  );
+}
diff --git a/ts/components/conversationList/MessageBodyHighlight.tsx b/ts/components/conversationList/MessageBodyHighlight.tsx
index af3d727eab..50fb166386 100644
--- a/ts/components/conversationList/MessageBodyHighlight.tsx
+++ b/ts/components/conversationList/MessageBodyHighlight.tsx
@@ -105,7 +105,7 @@ export class MessageBodyHighlight extends React.Component<Props> {
       const [, toHighlight] = match;
       count += 2;
       results.push(
-        <span className="module-message-body__highlight" key={count - 1}>
+        <span className="MessageBody__highlight" key={count - 1}>
           {renderEmoji({
             text: toHighlight,
             sizeClass,
diff --git a/ts/quill/mentions/matchers.ts b/ts/quill/mentions/matchers.ts
index a5b1dd7c15..2c52db7b5e 100644
--- a/ts/quill/mentions/matchers.ts
+++ b/ts/quill/mentions/matchers.ts
@@ -13,7 +13,7 @@ export const matchMention = (
   if (memberRepository) {
     const { title } = node.dataset;
 
-    if (node.classList.contains('module-message-body__at-mention')) {
+    if (node.classList.contains('MessageBody__at-mention')) {
       const { id } = node.dataset;
       const conversation = memberRepository.getMemberById(id);
 
diff --git a/ts/test-node/quill/mentions/matchers_test.ts b/ts/test-node/quill/mentions/matchers_test.ts
index 7fc9e44001..dd48dfcae8 100644
--- a/ts/test-node/quill/mentions/matchers_test.ts
+++ b/ts/test-node/quill/mentions/matchers_test.ts
@@ -32,7 +32,7 @@ const createMockElement = (
 
 const createMockAtMentionElement = (
   dataset: Record<string, string>
-): HTMLElement => createMockElement('module-message-body__at-mention', dataset);
+): HTMLElement => createMockElement('MessageBody__at-mention', dataset);
 
 const createMockMentionBlotElement = (
   dataset: Record<string, string>