diff --git a/web/components/contract-feed.tsx b/web/components/contract-feed.tsx
new file mode 100644
index 00000000..49671d4c
--- /dev/null
+++ b/web/components/contract-feed.tsx
@@ -0,0 +1,472 @@
+// From https://tailwindui.com/components/application-ui/lists/feeds
+import { useState } from 'react'
+import {
+  BanIcon,
+  ChatAltIcon,
+  CheckIcon,
+  LockClosedIcon,
+  StarIcon,
+  ThumbDownIcon,
+  ThumbUpIcon,
+  UserIcon,
+  UsersIcon,
+  XIcon,
+} from '@heroicons/react/solid'
+import { useBets } from '../hooks/use-bets'
+import { Bet } from '../lib/firebase/bets'
+import { Comment, mapCommentsByBetId } from '../lib/firebase/comments'
+import dayjs from 'dayjs'
+import relativeTime from 'dayjs/plugin/relativeTime'
+import { OutcomeLabel } from './outcome-label'
+import { Contract, setContract } from '../lib/firebase/contracts'
+import { useUser } from '../hooks/use-user'
+import { Linkify } from './linkify'
+import { Row } from './layout/row'
+import { createComment } from '../lib/firebase/comments'
+import { useComments } from '../hooks/use-comments'
+dayjs.extend(relativeTime)
+
+function FeedComment(props: { activityItem: any }) {
+  const { activityItem } = props
+  const { person, text, amount, outcome, createdTime } = activityItem
+  return (
+    <>
+      <div className="relative">
+        <img
+          className="h-10 w-10 rounded-full bg-gray-400 flex items-center justify-center ring-8 ring-gray-50"
+          src={person.avatarUrl}
+          alt=""
+        />
+
+        <span className="absolute -bottom-3 -right-2 bg-gray-50 rounded-tl px-0.5 py-px">
+          <ChatAltIcon className="h-5 w-5 text-gray-400" aria-hidden="true" />
+        </span>
+      </div>
+      <div className="min-w-0 flex-1">
+        <div>
+          <p className="mt-0.5 text-sm text-gray-500">
+            <a href={person.href} className="font-medium text-gray-900">
+              {person.name}
+            </a>{' '}
+            placed M$ {amount} on <OutcomeLabel outcome={outcome} />{' '}
+            <Timestamp time={createdTime} />
+          </p>
+        </div>
+        <div className="mt-2 text-gray-700">
+          <p className="whitespace-pre-wrap">
+            <Linkify text={text} />
+          </p>
+        </div>
+      </div>
+    </>
+  )
+}
+
+function Timestamp(props: { time: number }) {
+  const { time } = props
+  return (
+    <span
+      className="whitespace-nowrap text-gray-300"
+      title={dayjs(time).format('MMM D, h:mma')}
+    >
+      {dayjs(time).fromNow()}
+    </span>
+  )
+}
+
+function FeedBet(props: { activityItem: any }) {
+  const { activityItem } = props
+  const { id, contractId, amount, outcome, createdTime } = activityItem
+  const user = useUser()
+  const isCreator = user?.id == activityItem.userId
+
+  const [comment, setComment] = useState('')
+  async function submitComment() {
+    if (!user || !comment) return
+    await createComment(contractId, id, comment, user)
+  }
+  return (
+    <>
+      <div>
+        <div className="relative px-1">
+          <div className="h-8 w-8 bg-gray-200 rounded-full ring-8 ring-gray-50 flex items-center justify-center">
+            <UserIcon className="h-5 w-5 text-gray-500" aria-hidden="true" />
+          </div>
+        </div>
+      </div>
+      <div className="min-w-0 flex-1 py-1.5">
+        <div className="text-sm text-gray-500">
+          <span className="text-gray-900">
+            {isCreator ? 'You' : 'A trader'}
+          </span>{' '}
+          placed M$ {amount} on <OutcomeLabel outcome={outcome} />{' '}
+          <Timestamp time={createdTime} />
+          {isCreator && (
+            // Allow user to comment in an textarea if they are the creator
+            <div className="mt-2">
+              <textarea
+                value={comment}
+                onChange={(e) => setComment(e.target.value)}
+                className="textarea textarea-bordered w-full"
+                placeholder="Add a comment..."
+              />
+              <button
+                className="btn btn-outline btn-sm mt-1"
+                onClick={submitComment}
+              >
+                Comment
+              </button>
+            </div>
+          )}
+        </div>
+      </div>
+    </>
+  )
+}
+
+export function ContractDescription(props: {
+  contract: Contract
+  isCreator: boolean
+}) {
+  const { contract, isCreator } = props
+  const [editing, setEditing] = useState(false)
+  const editStatement = () => `${dayjs().format('MMM D, h:mma')}: `
+  const [description, setDescription] = useState(editStatement())
+
+  // Append the new description (after a newline)
+  async function saveDescription(e: any) {
+    e.preventDefault()
+    setEditing(false)
+    contract.description = `${contract.description}\n${description}`.trim()
+    await setContract(contract)
+    setDescription(editStatement())
+  }
+
+  return (
+    <div className="whitespace-pre-line break-words mt-2 text-gray-700">
+      <Linkify text={contract.description} />
+      <br />
+      {isCreator &&
+        !contract.resolution &&
+        (editing ? (
+          <form className="mt-4">
+            <textarea
+              className="textarea h-24 textarea-bordered w-full mb-1"
+              value={description}
+              onChange={(e) => setDescription(e.target.value || '')}
+              autoFocus
+              onFocus={(e) =>
+                // Focus starts at end of description.
+                e.target.setSelectionRange(
+                  description.length,
+                  description.length
+                )
+              }
+            />
+            <Row className="gap-2">
+              <button
+                className="btn btn-neutral btn-outline btn-sm"
+                onClick={saveDescription}
+              >
+                Save
+              </button>
+              <button
+                className="btn btn-error btn-outline btn-sm"
+                onClick={() => setEditing(false)}
+              >
+                Cancel
+              </button>
+            </Row>
+          </form>
+        ) : (
+          <Row>
+            <button
+              className="btn btn-neutral btn-outline btn-sm mt-4"
+              onClick={() => setEditing(true)}
+            >
+              Add to description
+            </button>
+          </Row>
+        ))}
+    </div>
+  )
+}
+
+function FeedStart(props: { contract: Contract }) {
+  const { contract } = props
+  const user = useUser()
+  const isCreator = user?.id === contract.creatorId
+
+  return (
+    <>
+      <div>
+        <div className="relative px-1">
+          <div className="h-8 w-8 bg-gray-200 rounded-full ring-8 ring-gray-50 flex items-center justify-center">
+            <StarIcon className="h-5 w-5 text-gray-500" aria-hidden="true" />
+          </div>
+        </div>
+      </div>
+      <div className="min-w-0 flex-1 py-1.5">
+        <div className="text-sm text-gray-500">
+          <span className="text-gray-900">{contract.creatorName}</span> created
+          this market <Timestamp time={contract.createdTime} />
+        </div>
+        <ContractDescription contract={contract} isCreator={isCreator} />
+      </div>
+    </>
+  )
+}
+
+function OutcomeIcon(props: { outcome?: 'YES' | 'NO' | 'CANCEL' }) {
+  const { outcome } = props
+  switch (outcome) {
+    case 'YES':
+      return <CheckIcon className="h-5 w-5 text-gray-500" aria-hidden="true" />
+    case 'NO':
+      return <XIcon className="h-5 w-5 text-gray-500" aria-hidden="true" />
+    case 'CANCEL':
+    default:
+      return <BanIcon className="h-5 w-5 text-gray-500" aria-hidden="true" />
+  }
+}
+
+function FeedResolve(props: { contract: Contract }) {
+  const { contract } = props
+  const resolution = contract.resolution || 'CANCEL'
+
+  return (
+    <>
+      <div>
+        <div className="relative px-1">
+          <div className="h-8 w-8 bg-gray-200 rounded-full ring-8 ring-gray-50 flex items-center justify-center">
+            <OutcomeIcon outcome={resolution} />
+          </div>
+        </div>
+      </div>
+      <div className="min-w-0 flex-1 py-1.5">
+        <div className="text-sm text-gray-500">
+          <span className="text-gray-900">{contract.creatorName}</span> resolved
+          this market to <OutcomeLabel outcome={resolution} />{' '}
+          <Timestamp time={contract.resolutionTime || 0} />
+        </div>
+      </div>
+    </>
+  )
+}
+
+function FeedClose(props: { contract: Contract }) {
+  const { contract } = props
+
+  return (
+    <>
+      <div>
+        <div className="relative px-1">
+          <div className="h-8 w-8 bg-gray-200 rounded-full ring-8 ring-gray-50 flex items-center justify-center">
+            <LockClosedIcon
+              className="h-5 w-5 text-gray-500"
+              aria-hidden="true"
+            />
+          </div>
+        </div>
+      </div>
+      <div className="min-w-0 flex-1 py-1.5">
+        <div className="text-sm text-gray-500">
+          Trading closed in this market{' '}
+          <Timestamp time={contract.closeTime || 0} />
+        </div>
+      </div>
+    </>
+  )
+}
+
+function toFeedBet(bet: Bet) {
+  return {
+    id: bet.id,
+    contractId: bet.contractId,
+    userId: bet.userId,
+    type: 'bet',
+    amount: bet.amount,
+    outcome: bet.outcome,
+    createdTime: bet.createdTime,
+    date: dayjs(bet.createdTime).fromNow(),
+  }
+}
+
+function toFeedComment(bet: Bet, comment: Comment) {
+  return {
+    id: bet.id,
+    contractId: bet.contractId,
+    userId: bet.userId,
+    type: 'comment',
+    amount: bet.amount,
+    outcome: bet.outcome,
+    createdTime: bet.createdTime,
+    date: dayjs(bet.createdTime).fromNow(),
+
+    // Invariant: bet.comment exists
+    text: comment.text,
+    person: {
+      href: `/${comment.userUsername}`,
+      name: comment.userName,
+      avatarUrl: comment.userAvatarUrl,
+    },
+  }
+}
+
+// Group together bets that are:
+// - Within 24h of the first in the group
+// - Do not have a comment
+// - Were not created by this user
+// Return a list of ActivityItems
+function group(bets: Bet[], comments: Comment[], userId?: string) {
+  const commentsMap = mapCommentsByBetId(comments)
+  const items: any[] = []
+  let group: Bet[] = []
+
+  // Turn the current group into an ActivityItem
+  function pushGroup() {
+    if (group.length == 1) {
+      items.push(toActivityItem(group[0]))
+    } else if (group.length > 1) {
+      items.push({ type: 'betgroup', bets: [...group], id: group[0].id })
+    }
+    group = []
+  }
+
+  function toActivityItem(bet: Bet) {
+    const comment = commentsMap[bet.id]
+    return comment ? toFeedComment(bet, comment) : toFeedBet(bet)
+  }
+
+  for (const bet of bets) {
+    const isCreator = userId === bet.userId
+
+    if (commentsMap[bet.id] || isCreator) {
+      pushGroup()
+      // Create a single item for this
+      items.push(toActivityItem(bet))
+    } else {
+      if (
+        group.length > 0 &&
+        dayjs(bet.createdTime).diff(dayjs(group[0].createdTime), 'hour') > 24
+      ) {
+        // More than 24h has passed; start a new group
+        pushGroup()
+      }
+      group.push(bet)
+    }
+  }
+  if (group.length > 0) {
+    pushGroup()
+  }
+  return items as ActivityItem[]
+}
+
+// TODO: Make this expandable to show all grouped bets?
+function FeedBetGroup(props: { activityItem: any }) {
+  const { activityItem } = props
+  const bets: Bet[] = activityItem.bets
+
+  const yesAmount = bets
+    .filter((b) => b.outcome == 'YES')
+    .reduce((acc, bet) => acc + bet.amount, 0)
+  const yesSpan = yesAmount ? (
+    <span>
+      M$ {yesAmount} on <OutcomeLabel outcome={'YES'} />
+    </span>
+  ) : null
+  const noAmount = bets
+    .filter((b) => b.outcome == 'NO')
+    .reduce((acc, bet) => acc + bet.amount, 0)
+  const noSpan = noAmount ? (
+    <span>
+      M$ {noAmount} on <OutcomeLabel outcome={'NO'} />
+    </span>
+  ) : null
+  const traderCount = bets.length
+  const createdTime = bets[0].createdTime
+
+  return (
+    <>
+      <div>
+        <div className="relative px-1">
+          <div className="h-8 w-8 bg-gray-200 rounded-full ring-8 ring-gray-50 flex items-center justify-center">
+            <UsersIcon className="h-5 w-5 text-gray-500" aria-hidden="true" />
+          </div>
+        </div>
+      </div>
+      <div className="min-w-0 flex-1 py-1.5">
+        <div className="text-sm text-gray-500">
+          <span className="text-gray-900">{traderCount} traders</span> placed{' '}
+          {yesSpan}
+          {yesAmount && noAmount ? ' and ' : ''}
+          {noSpan} <Timestamp time={createdTime} />
+        </div>
+      </div>
+    </>
+  )
+}
+
+// Missing feed items:
+// - Bet sold?
+type ActivityItem = {
+  id: string
+  type: 'bet' | 'comment' | 'start' | 'betgroup' | 'close' | 'resolve'
+}
+
+export function ContractFeed(props: { contract: Contract }) {
+  const { contract } = props
+  const { id } = contract
+  const user = useUser()
+
+  let bets = useBets(id)
+  if (bets === 'loading') bets = []
+
+  let comments = useComments(id)
+  if (comments === 'loading') comments = []
+
+  const allItems = [
+    { type: 'start', id: 0 },
+    ...group(bets, comments, user?.id),
+  ]
+  if (contract.closeTime) {
+    allItems.push({ type: 'close', id: `${contract.closeTime}` })
+  }
+  if (contract.resolution) {
+    allItems.push({ type: 'resolve', id: `${contract.resolutionTime}` })
+  }
+
+  return (
+    <div className="flow-root">
+      <ul role="list" className="-mb-8">
+        {allItems.map((activityItem, activityItemIdx) => (
+          <li key={activityItem.id}>
+            <div className="relative pb-8">
+              {activityItemIdx !== allItems.length - 1 ? (
+                <span
+                  className="absolute top-5 left-5 -ml-px h-full w-0.5 bg-gray-200"
+                  aria-hidden="true"
+                />
+              ) : null}
+              <div className="relative flex items-start space-x-3">
+                {activityItem.type === 'start' ? (
+                  <FeedStart contract={contract} />
+                ) : activityItem.type === 'comment' ? (
+                  <FeedComment activityItem={activityItem} />
+                ) : activityItem.type === 'bet' ? (
+                  <FeedBet activityItem={activityItem} />
+                ) : activityItem.type === 'betgroup' ? (
+                  <FeedBetGroup activityItem={activityItem} />
+                ) : activityItem.type === 'close' ? (
+                  <FeedClose contract={contract} />
+                ) : activityItem.type === 'resolve' ? (
+                  <FeedResolve contract={contract} />
+                ) : null}
+              </div>
+            </div>
+          </li>
+        ))}
+      </ul>
+    </div>
+  )
+}
diff --git a/web/components/contract-overview.tsx b/web/components/contract-overview.tsx
index 114ba9b9..85dd97df 100644
--- a/web/components/contract-overview.tsx
+++ b/web/components/contract-overview.tsx
@@ -1,10 +1,4 @@
-import { useState } from 'react'
-import {
-  compute,
-  Contract,
-  deleteContract,
-  setContract,
-} from '../lib/firebase/contracts'
+import { compute, Contract, deleteContract } from '../lib/firebase/contracts'
 import { Col } from './layout/col'
 import { Spacer } from './layout/spacer'
 import { ContractProbGraph } from './contract-prob-graph'
@@ -15,6 +9,7 @@ import dayjs from 'dayjs'
 import { Linkify } from './linkify'
 import clsx from 'clsx'
 import { ContractDetails, ResolutionOrChance } from './contract-card'
+import { ContractFeed } from './contract-feed'
 
 function ContractCloseTime(props: { contract: Contract }) {
   const closeTime = props.contract.closeTime
@@ -29,74 +24,6 @@ function ContractCloseTime(props: { contract: Contract }) {
   )
 }
 
-function ContractDescription(props: {
-  contract: Contract
-  isCreator: boolean
-}) {
-  const { contract, isCreator } = props
-  const [editing, setEditing] = useState(false)
-  const editStatement = () => `${dayjs().format('MMM D, h:mma')}: `
-  const [description, setDescription] = useState(editStatement())
-
-  // Append the new description (after a newline)
-  async function saveDescription(e: any) {
-    e.preventDefault()
-    setEditing(false)
-    contract.description = `${contract.description}\n${description}`.trim()
-    await setContract(contract)
-    setDescription(editStatement())
-  }
-
-  return (
-    <div className="whitespace-pre-line break-words">
-      <Linkify text={contract.description} />
-      <br />
-      {isCreator &&
-        !contract.resolution &&
-        (editing ? (
-          <form className="mt-4">
-            <textarea
-              className="textarea h-24 textarea-bordered w-full mb-2"
-              value={description}
-              onChange={(e) => setDescription(e.target.value || '')}
-              autoFocus
-              onFocus={(e) =>
-                // Focus starts at end of description.
-                e.target.setSelectionRange(
-                  description.length,
-                  description.length
-                )
-              }
-            />
-            <Row className="gap-4 justify-end">
-              <button
-                className="btn btn-error btn-outline btn-sm mt-2"
-                onClick={() => setEditing(false)}
-              >
-                Cancel
-              </button>
-              <button
-                className="btn btn-neutral btn-outline btn-sm mt-2"
-                onClick={saveDescription}
-              >
-                Save
-              </button>
-            </Row>
-          </form>
-        ) : (
-          <Row className="justify-end">
-            <button
-              className="btn btn-neutral btn-outline btn-sm mt-4"
-              onClick={() => setEditing(true)}
-            >
-              Add to description
-            </button>
-          </Row>
-        ))}
-    </div>
-  )
-}
-
 export const ContractOverview = (props: {
   contract: Contract
   className?: string
@@ -142,14 +69,6 @@ export const ContractOverview = (props: {
 
       <ContractCloseTime contract={contract} />
 
-      <Spacer h={4} />
-
-      {((isCreator && !contract.resolution) || contract.description) && (
-        <label className="text-gray-500 mb-2 text-sm">Description</label>
-      )}
-
-      <ContractDescription contract={contract} isCreator={isCreator} />
-
       {/* Show a delete button for contracts without any trading */}
       {isCreator && truePool === 0 && (
         <>
@@ -166,6 +85,10 @@ export const ContractOverview = (props: {
           </button>
         </>
       )}
+
+      <Spacer h={4} />
+
+      <ContractFeed contract={contract} />
     </Col>
   )
 }
diff --git a/web/hooks/use-comments.ts b/web/hooks/use-comments.ts
new file mode 100644
index 00000000..0a9dead3
--- /dev/null
+++ b/web/hooks/use-comments.ts
@@ -0,0 +1,12 @@
+import { useEffect, useState } from 'react'
+import { Comment, listenForComments } from '../lib/firebase/comments'
+
+export const useComments = (contractId: string) => {
+  const [comments, setComments] = useState<Comment[] | 'loading'>('loading')
+
+  useEffect(() => {
+    if (contractId) return listenForComments(contractId, setComments)
+  }, [contractId])
+
+  return comments
+}
diff --git a/web/lib/firebase/bets.ts b/web/lib/firebase/bets.ts
index b09d8f8b..49d92e0e 100644
--- a/web/lib/firebase/bets.ts
+++ b/web/lib/firebase/bets.ts
@@ -22,6 +22,7 @@ export type Bet = {
   sale?: {
     amount: number // amount user makes from sale
     betId: string // id of bet being sold
+    // TODO: add sale time?
   }
 
   isSold?: boolean // true if this BUY bet has been sold
diff --git a/web/lib/firebase/comments.ts b/web/lib/firebase/comments.ts
new file mode 100644
index 00000000..d46c6ee9
--- /dev/null
+++ b/web/lib/firebase/comments.ts
@@ -0,0 +1,60 @@
+import { doc, collection, onSnapshot, setDoc } from 'firebase/firestore'
+import { db } from './init'
+import { User } from './users'
+
+// Currently, comments are created after the bet, not atomically with the bet.
+// They're uniquely identified by the pair contractId/betId.
+export type Comment = {
+  contractId: string
+  betId: string
+  text: string
+  createdTime: number
+  // Denormalized, for rendering comments
+  userName?: string
+  userUsername?: string
+  userAvatarUrl?: string
+}
+
+export async function createComment(
+  contractId: string,
+  betId: string,
+  text: string,
+  commenter: User
+) {
+  const ref = doc(getCommentsCollection(contractId), betId)
+  return await setDoc(ref, {
+    contractId,
+    betId,
+    text,
+    createdTime: Date.now(),
+    userName: commenter.name,
+    userUsername: commenter.username,
+    userAvatarUrl: commenter.avatarUrl,
+  })
+}
+
+function getCommentsCollection(contractId: string) {
+  return collection(db, 'contracts', contractId, 'comments')
+}
+
+export function listenForComments(
+  contractId: string,
+  setComments: (comments: Comment[]) => void
+) {
+  return onSnapshot(getCommentsCollection(contractId), (snap) => {
+    const comments = snap.docs.map((doc) => doc.data() as Comment)
+
+    comments.sort((c1, c2) => c1.createdTime - c2.createdTime)
+
+    setComments(comments)
+  })
+}
+
+// Return a map of betId -> comment
+export function mapCommentsByBetId(comments: Comment[]) {
+  const map: Record<string, Comment> = {}
+  for (const comment of comments) {
+    map[comment.betId] = comment
+  }
+  return map
+}