diff --git a/prisma/migrations/20240414135355_add_activity_log/migration.sql b/prisma/migrations/20240414135355_add_activity_log/migration.sql
new file mode 100644
index 0000000..a7d03ba
--- /dev/null
+++ b/prisma/migrations/20240414135355_add_activity_log/migration.sql
@@ -0,0 +1,18 @@
+-- CreateEnum
+CREATE TYPE "ActivityType" AS ENUM ('UPDATE_GROUP', 'CREATE_EXPENSE', 'UPDATE_EXPENSE', 'DELETE_EXPENSE');
+
+-- CreateTable
+CREATE TABLE "Activity" (
+    "id" TEXT NOT NULL,
+    "groupId" TEXT NOT NULL,
+    "time" TIMESTAMP(3) NOT NULL DEFAULT CURRENT_TIMESTAMP,
+    "activityType" "ActivityType" NOT NULL,
+    "participantId" TEXT,
+    "expenseId" TEXT,
+    "data" TEXT,
+
+    CONSTRAINT "Activity_pkey" PRIMARY KEY ("id")
+);
+
+-- AddForeignKey
+ALTER TABLE "Activity" ADD CONSTRAINT "Activity_groupId_fkey" FOREIGN KEY ("groupId") REFERENCES "Group"("id") ON DELETE RESTRICT ON UPDATE CASCADE;
diff --git a/prisma/schema.prisma b/prisma/schema.prisma
index f738947..2989f3c 100644
--- a/prisma/schema.prisma
+++ b/prisma/schema.prisma
@@ -17,6 +17,7 @@ model Group {
   currency     String        @default("$")
   participants Participant[]
   expenses     Expense[]
+  activities   Activity[]
   createdAt    DateTime      @default(now())
 }
 
@@ -80,3 +81,21 @@ model ExpensePaidFor {
 
   @@id([expenseId, participantId])
 }
+
+model Activity {
+  id            String       @id
+  group         Group        @relation(fields: [groupId], references: [id])
+  groupId       String
+  time          DateTime     @default(now())
+  activityType  ActivityType
+  participantId String?
+  expenseId     String?
+  data          String?
+}
+
+enum ActivityType {
+  UPDATE_GROUP
+  CREATE_EXPENSE
+  UPDATE_EXPENSE
+  DELETE_EXPENSE
+}
diff --git a/src/app/groups/[groupId]/activity/activity-item.tsx b/src/app/groups/[groupId]/activity/activity-item.tsx
new file mode 100644
index 0000000..6fdc469
--- /dev/null
+++ b/src/app/groups/[groupId]/activity/activity-item.tsx
@@ -0,0 +1,102 @@
+'use client'
+import { Button } from '@/components/ui/button'
+import { getGroupExpenses } from '@/lib/api'
+import { DateTimeStyle, cn, formatDate } from '@/lib/utils'
+import { Activity, ActivityType, Participant } from '@prisma/client'
+import { ChevronRight } from 'lucide-react'
+import Link from 'next/link'
+import { useRouter } from 'next/navigation'
+
+type Props = {
+  groupId: string
+  activity: Activity
+  participant?: Participant
+  expense?: Awaited<ReturnType<typeof getGroupExpenses>>[number]
+  dateStyle: DateTimeStyle
+}
+
+function getSummary(activity: Activity, participantName?: string) {
+  const participant = participantName ?? 'Someone'
+  const expense = activity.data ?? ''
+  if (activity.activityType == ActivityType.UPDATE_GROUP) {
+    return (
+      <>
+        Group settings were modified by <strong>{participant}</strong>
+      </>
+    )
+  } else if (activity.activityType == ActivityType.CREATE_EXPENSE) {
+    return (
+      <>
+        Expense <em>&ldquo;{expense}&rdquo;</em> created by{' '}
+        <strong>{participant}</strong>.
+      </>
+    )
+  } else if (activity.activityType == ActivityType.UPDATE_EXPENSE) {
+    return (
+      <>
+        Expense <em>&ldquo;{expense}&rdquo;</em> updated by{' '}
+        <strong>{participant}</strong>.
+      </>
+    )
+  } else if (activity.activityType == ActivityType.DELETE_EXPENSE) {
+    return (
+      <>
+        Expense <em>&ldquo;{expense}&rdquo;</em> deleted by{' '}
+        <strong>{participant}</strong>.
+      </>
+    )
+  }
+}
+
+export function ActivityItem({
+  groupId,
+  activity,
+  participant,
+  expense,
+  dateStyle,
+}: Props) {
+  const router = useRouter()
+
+  const expenseExists = expense !== undefined
+  const summary = getSummary(activity, participant?.name)
+
+  return (
+    <div
+      className={cn(
+        'flex justify-between sm:rounded-lg px-2 sm:pr-1 sm:pl-2 py-2 text-sm hover:bg-accent gap-1 items-stretch',
+        expenseExists && 'cursor-pointer',
+      )}
+      onClick={() => {
+        if (expenseExists) {
+          router.push(`/groups/${groupId}/expenses/${activity.expenseId}/edit`)
+        }
+      }}
+    >
+      <div className="flex flex-col justify-between items-start">
+        {dateStyle !== undefined && (
+          <div className="mt-1 text-xs/5 text-muted-foreground">
+            {formatDate(activity.time, { dateStyle })}
+          </div>
+        )}
+        <div className="my-1 text-xs/5 text-muted-foreground">
+          {formatDate(activity.time, { timeStyle: 'short' })}
+        </div>
+      </div>
+      <div className="flex-1">
+        <div className="m-1">{summary}</div>
+      </div>
+      {expenseExists && (
+        <Button
+          size="icon"
+          variant="link"
+          className="self-center hidden sm:flex w-5 h-5"
+          asChild
+        >
+          <Link href={`/groups/${groupId}/expenses/${activity.expenseId}/edit`}>
+            <ChevronRight className="w-4 h-4" />
+          </Link>
+        </Button>
+      )}
+    </div>
+  )
+}
diff --git a/src/app/groups/[groupId]/activity/activity-list.tsx b/src/app/groups/[groupId]/activity/activity-list.tsx
new file mode 100644
index 0000000..1cde768
--- /dev/null
+++ b/src/app/groups/[groupId]/activity/activity-list.tsx
@@ -0,0 +1,112 @@
+import { ActivityItem } from '@/app/groups/[groupId]/activity/activity-item'
+import { getGroupExpenses } from '@/lib/api'
+import { Activity, Participant } from '@prisma/client'
+import dayjs, { type Dayjs } from 'dayjs'
+
+type Props = {
+  groupId: string
+  participants: Participant[]
+  expenses: Awaited<ReturnType<typeof getGroupExpenses>>
+  activities: Activity[]
+}
+
+const DATE_GROUPS = {
+  TODAY: 'Today',
+  YESTERDAY: 'Yesterday',
+  EARLIER_THIS_WEEK: 'Earlier this week',
+  LAST_WEEK: 'Last week',
+  EARLIER_THIS_MONTH: 'Earlier this month',
+  LAST_MONTH: 'Last month',
+  EARLIER_THIS_YEAR: 'Earlier this year',
+  LAST_YEAR: 'Last year',
+  OLDER: 'Older',
+}
+
+function getDateGroup(date: Dayjs, today: Dayjs) {
+  if (today.isSame(date, 'day')) {
+    return DATE_GROUPS.TODAY
+  } else if (today.subtract(1, 'day').isSame(date, 'day')) {
+    return DATE_GROUPS.YESTERDAY
+  } else if (today.isSame(date, 'week')) {
+    return DATE_GROUPS.EARLIER_THIS_WEEK
+  } else if (today.subtract(1, 'week').isSame(date, 'week')) {
+    return DATE_GROUPS.LAST_WEEK
+  } else if (today.isSame(date, 'month')) {
+    return DATE_GROUPS.EARLIER_THIS_MONTH
+  } else if (today.subtract(1, 'month').isSame(date, 'month')) {
+    return DATE_GROUPS.LAST_MONTH
+  } else if (today.isSame(date, 'year')) {
+    return DATE_GROUPS.EARLIER_THIS_YEAR
+  } else if (today.subtract(1, 'year').isSame(date, 'year')) {
+    return DATE_GROUPS.LAST_YEAR
+  } else {
+    return DATE_GROUPS.OLDER
+  }
+}
+
+function getGroupedActivitiesByDate(activities: Activity[]) {
+  const today = dayjs()
+  return activities.reduce(
+    (result: { [key: string]: Activity[] }, activity: Activity) => {
+      const activityGroup = getDateGroup(dayjs(activity.time), today)
+      result[activityGroup] = result[activityGroup] ?? []
+      result[activityGroup].push(activity)
+      return result
+    },
+    {},
+  )
+}
+
+export function ActivityList({
+  groupId,
+  participants,
+  expenses,
+  activities,
+}: Props) {
+  const groupedActivitiesByDate = getGroupedActivitiesByDate(activities)
+
+  return activities.length > 0 ? (
+    <>
+      {Object.values(DATE_GROUPS).map((dateGroup: string) => {
+        let groupActivities = groupedActivitiesByDate[dateGroup]
+        if (!groupActivities || groupActivities.length === 0) return null
+        const dateStyle =
+          dateGroup == DATE_GROUPS.TODAY || dateGroup == DATE_GROUPS.YESTERDAY
+            ? undefined
+            : 'medium'
+
+        return (
+          <div key={dateGroup}>
+            <div
+              className={
+                'text-muted-foreground text-xs py-1 font-semibold sticky top-16 bg-white dark:bg-[#1b1917]'
+              }
+            >
+              {dateGroup}
+            </div>
+            {groupActivities.map((activity: Activity) => {
+              const participant =
+                activity.participantId !== null
+                  ? participants.find((p) => p.id === activity.participantId)
+                  : undefined
+              const expense =
+                activity.expenseId !== null
+                  ? expenses.find((e) => e.id === activity.expenseId)
+                  : undefined
+              return (
+                <ActivityItem
+                  key={activity.id}
+                  {...{ groupId, activity, participant, expense, dateStyle }}
+                />
+              )
+            })}
+          </div>
+        )
+      })}
+    </>
+  ) : (
+    <p className="px-6 text-sm py-6">
+      There is not yet any activity in your group.
+    </p>
+  )
+}
diff --git a/src/app/groups/[groupId]/activity/page.tsx b/src/app/groups/[groupId]/activity/page.tsx
new file mode 100644
index 0000000..9fbe890
--- /dev/null
+++ b/src/app/groups/[groupId]/activity/page.tsx
@@ -0,0 +1,51 @@
+import { cached } from '@/app/cached-functions'
+import { ActivityList } from '@/app/groups/[groupId]/activity/activity-list'
+import {
+  Card,
+  CardContent,
+  CardDescription,
+  CardHeader,
+  CardTitle,
+} from '@/components/ui/card'
+import { getActivities, getGroupExpenses } from '@/lib/api'
+import { Metadata } from 'next'
+import { notFound } from 'next/navigation'
+
+export const metadata: Metadata = {
+  title: 'Activity',
+}
+
+export default async function ActivityPage({
+  params: { groupId },
+}: {
+  params: { groupId: string }
+}) {
+  const group = await cached.getGroup(groupId)
+  if (!group) notFound()
+
+  const expenses = await getGroupExpenses(groupId)
+  const activities = await getActivities(groupId)
+
+  return (
+    <>
+      <Card className="mb-4">
+        <CardHeader>
+          <CardTitle>Activity</CardTitle>
+          <CardDescription>
+            Overview of all activity in this group.
+          </CardDescription>
+        </CardHeader>
+        <CardContent className="flex flex-col space-y-4">
+          <ActivityList
+            {...{
+              groupId,
+              participants: group.participants,
+              expenses,
+              activities,
+            }}
+          />
+        </CardContent>
+      </Card>
+    </>
+  )
+}
diff --git a/src/app/groups/[groupId]/edit/page.tsx b/src/app/groups/[groupId]/edit/page.tsx
index c174c37..ab2318f 100644
--- a/src/app/groups/[groupId]/edit/page.tsx
+++ b/src/app/groups/[groupId]/edit/page.tsx
@@ -17,10 +17,10 @@ export default async function EditGroupPage({
   const group = await cached.getGroup(groupId)
   if (!group) notFound()
 
-  async function updateGroupAction(values: unknown) {
+  async function updateGroupAction(values: unknown, participantId?: string) {
     'use server'
     const groupFormValues = groupFormSchema.parse(values)
-    const group = await updateGroup(groupId, groupFormValues)
+    const group = await updateGroup(groupId, groupFormValues, participantId)
     redirect(`/groups/${group.id}`)
   }
 
diff --git a/src/app/groups/[groupId]/expenses/[expenseId]/edit/page.tsx b/src/app/groups/[groupId]/expenses/[expenseId]/edit/page.tsx
index 2514a77..a91de1f 100644
--- a/src/app/groups/[groupId]/expenses/[expenseId]/edit/page.tsx
+++ b/src/app/groups/[groupId]/expenses/[expenseId]/edit/page.tsx
@@ -27,16 +27,16 @@ export default async function EditExpensePage({
   const expense = await getExpense(groupId, expenseId)
   if (!expense) notFound()
 
-  async function updateExpenseAction(values: unknown) {
+  async function updateExpenseAction(values: unknown, participantId?: string) {
     'use server'
     const expenseFormValues = expenseFormSchema.parse(values)
-    await updateExpense(groupId, expenseId, expenseFormValues)
+    await updateExpense(groupId, expenseId, expenseFormValues, participantId)
     redirect(`/groups/${groupId}`)
   }
 
-  async function deleteExpenseAction() {
+  async function deleteExpenseAction(participantId?: string) {
     'use server'
-    await deleteExpense(expenseId)
+    await deleteExpense(groupId, expenseId, participantId)
     redirect(`/groups/${groupId}`)
   }
 
diff --git a/src/app/groups/[groupId]/expenses/create-from-receipt-button.tsx b/src/app/groups/[groupId]/expenses/create-from-receipt-button.tsx
index dab04a1..680fe33 100644
--- a/src/app/groups/[groupId]/expenses/create-from-receipt-button.tsx
+++ b/src/app/groups/[groupId]/expenses/create-from-receipt-button.tsx
@@ -26,7 +26,7 @@ import {
 import { ToastAction } from '@/components/ui/toast'
 import { useToast } from '@/components/ui/use-toast'
 import { useMediaQuery } from '@/lib/hooks'
-import { formatCurrency, formatExpenseDate, formatFileSize } from '@/lib/utils'
+import { formatCurrency, formatDate, formatFileSize } from '@/lib/utils'
 import { Category } from '@prisma/client'
 import { ChevronRight, FileQuestion, Loader2, Receipt } from 'lucide-react'
 import { getImageData, usePresignedUpload } from 'next-s3-upload'
@@ -212,9 +212,9 @@ export function CreateFromReceiptButton({
               <div>
                 {receiptInfo ? (
                   receiptInfo.date ? (
-                    formatExpenseDate(
-                      new Date(`${receiptInfo?.date}T12:00:00.000Z`),
-                    )
+                    formatDate(new Date(`${receiptInfo?.date}T12:00:00.000Z`), {
+                      dateStyle: 'medium',
+                    })
                   ) : (
                     <Unknown />
                   )
diff --git a/src/app/groups/[groupId]/expenses/create/page.tsx b/src/app/groups/[groupId]/expenses/create/page.tsx
index 6398fd1..3ca3b36 100644
--- a/src/app/groups/[groupId]/expenses/create/page.tsx
+++ b/src/app/groups/[groupId]/expenses/create/page.tsx
@@ -20,10 +20,10 @@ export default async function ExpensePage({
   const group = await cached.getGroup(groupId)
   if (!group) notFound()
 
-  async function createExpenseAction(values: unknown) {
+  async function createExpenseAction(values: unknown, participantId?: string) {
     'use server'
     const expenseFormValues = expenseFormSchema.parse(values)
-    await createExpense(expenseFormValues, groupId)
+    await createExpense(expenseFormValues, groupId, participantId)
     redirect(`/groups/${groupId}`)
   }
 
diff --git a/src/app/groups/[groupId]/expenses/expense-card.tsx b/src/app/groups/[groupId]/expenses/expense-card.tsx
index 8ea6063..f4a5f28 100644
--- a/src/app/groups/[groupId]/expenses/expense-card.tsx
+++ b/src/app/groups/[groupId]/expenses/expense-card.tsx
@@ -3,7 +3,7 @@ import { ActiveUserBalance } from '@/app/groups/[groupId]/expenses/active-user-b
 import { CategoryIcon } from '@/app/groups/[groupId]/expenses/category-icon'
 import { Button } from '@/components/ui/button'
 import { getGroupExpenses } from '@/lib/api'
-import { cn, formatCurrency, formatExpenseDate } from '@/lib/utils'
+import { cn, formatCurrency, formatDate } from '@/lib/utils'
 import { ChevronRight } from 'lucide-react'
 import Link from 'next/link'
 import { useRouter } from 'next/navigation'
@@ -60,7 +60,7 @@ export function ExpenseCard({ expense, currency, groupId }: Props) {
           {formatCurrency(currency, expense.amount)}
         </div>
         <div className="text-xs text-muted-foreground">
-          {formatExpenseDate(expense.expenseDate)}
+          {formatDate(expense.expenseDate, { dateStyle: 'medium' })}
         </div>
       </div>
       <Button
diff --git a/src/app/groups/[groupId]/group-tabs.tsx b/src/app/groups/[groupId]/group-tabs.tsx
index d7a0876..002724c 100644
--- a/src/app/groups/[groupId]/group-tabs.tsx
+++ b/src/app/groups/[groupId]/group-tabs.tsx
@@ -15,7 +15,7 @@ export function GroupTabs({ groupId }: Props) {
   return (
     <Tabs
       value={value}
-      className="[&>*]:border"
+      className="[&>*]:border overflow-x-auto"
       onValueChange={(value) => {
         router.push(`/groups/${groupId}/${value}`)
       }}
@@ -24,6 +24,7 @@ export function GroupTabs({ groupId }: Props) {
         <TabsTrigger value="expenses">Expenses</TabsTrigger>
         <TabsTrigger value="balances">Balances</TabsTrigger>
         <TabsTrigger value="stats">Stats</TabsTrigger>
+        <TabsTrigger value="activity">Activity</TabsTrigger>
         <TabsTrigger value="edit">Settings</TabsTrigger>
       </TabsList>
     </Tabs>
diff --git a/src/app/groups/[groupId]/layout.tsx b/src/app/groups/[groupId]/layout.tsx
index cb31df7..919f71e 100644
--- a/src/app/groups/[groupId]/layout.tsx
+++ b/src/app/groups/[groupId]/layout.tsx
@@ -35,7 +35,7 @@ export default async function GroupLayout({
 
   return (
     <>
-      <div className="flex flex-col sm:flex-row justify-between sm:items-center gap-3">
+      <div className="flex flex-col justify-between gap-3">
         <h1 className="font-bold text-2xl">
           <Link href={`/groups/${groupId}`}>{group.name}</Link>
         </h1>
diff --git a/src/app/groups/[groupId]/share-button.tsx b/src/app/groups/[groupId]/share-button.tsx
index d5dd350..9addb29 100644
--- a/src/app/groups/[groupId]/share-button.tsx
+++ b/src/app/groups/[groupId]/share-button.tsx
@@ -23,7 +23,7 @@ export function ShareButton({ group }: Props) {
   return (
     <Popover>
       <PopoverTrigger asChild>
-        <Button title="Share" size="icon">
+        <Button title="Share" size="icon" className="flex-shrink-0">
           <Share className="w-4 h-4" />
         </Button>
       </PopoverTrigger>
diff --git a/src/components/expense-form.tsx b/src/components/expense-form.tsx
index f68dc50..fbc0099 100644
--- a/src/components/expense-form.tsx
+++ b/src/components/expense-form.tsx
@@ -35,6 +35,7 @@ import {
 } from '@/components/ui/select'
 import { getCategories, getExpense, getGroup, randomId } from '@/lib/api'
 import { RuntimeFeatureFlags } from '@/lib/featureFlags'
+import { useActiveUser } from '@/lib/hooks'
 import {
   ExpenseFormValues,
   SplittingOptions,
@@ -56,8 +57,8 @@ export type Props = {
   group: NonNullable<Awaited<ReturnType<typeof getGroup>>>
   expense?: NonNullable<Awaited<ReturnType<typeof getExpense>>>
   categories: NonNullable<Awaited<ReturnType<typeof getCategories>>>
-  onSubmit: (values: ExpenseFormValues) => Promise<void>
-  onDelete?: () => Promise<void>
+  onSubmit: (values: ExpenseFormValues, participantId?: string) => Promise<void>
+  onDelete?: (participantId?: string) => Promise<void>
   runtimeFeatureFlags: RuntimeFeatureFlags
 }
 
@@ -235,10 +236,11 @@ export function ExpenseForm({
         },
   })
   const [isCategoryLoading, setCategoryLoading] = useState(false)
+  const activeUserId = useActiveUser(group.id)
 
   const submit = async (values: ExpenseFormValues) => {
     await persistDefaultSplittingOptions(group.id, values)
-    return onSubmit(values)
+    return onSubmit(values, activeUserId ?? undefined)
   }
 
   return (
@@ -722,7 +724,9 @@ export function ExpenseForm({
             {isCreate ? <>Create</> : <>Save</>}
           </SubmitButton>
           {!isCreate && onDelete && (
-            <DeletePopup onDelete={onDelete}></DeletePopup>
+            <DeletePopup
+              onDelete={() => onDelete(activeUserId ?? undefined)}
+            ></DeletePopup>
           )}
           <Button variant="ghost" asChild>
             <Link href={`/groups/${group.id}`}>Cancel</Link>
diff --git a/src/components/group-form.tsx b/src/components/group-form.tsx
index 886070c..87efbcc 100644
--- a/src/components/group-form.tsx
+++ b/src/components/group-form.tsx
@@ -41,7 +41,10 @@ import { useFieldArray, useForm } from 'react-hook-form'
 
 export type Props = {
   group?: NonNullable<Awaited<ReturnType<typeof getGroup>>>
-  onSubmit: (groupFormValues: GroupFormValues) => Promise<void>
+  onSubmit: (
+    groupFormValues: GroupFormValues,
+    participantId?: string,
+  ) => Promise<void>
   protectedParticipantIds?: string[]
 }
 
@@ -99,7 +102,11 @@ export function GroupForm({
     <Form {...form}>
       <form
         onSubmit={form.handleSubmit(async (values) => {
-          await onSubmit(values)
+          await onSubmit(
+            values,
+            group?.participants.find((p) => p.name === activeUser)?.id ??
+              undefined,
+          )
         })}
       >
         <Card className="mb-4">
diff --git a/src/lib/api.ts b/src/lib/api.ts
index 39910e1..a592ada 100644
--- a/src/lib/api.ts
+++ b/src/lib/api.ts
@@ -1,6 +1,6 @@
 import { prisma } from '@/lib/prisma'
 import { ExpenseFormValues, GroupFormValues } from '@/lib/schemas'
-import { Expense } from '@prisma/client'
+import { ActivityType, Expense } from '@prisma/client'
 import { nanoid } from 'nanoid'
 
 export function randomId() {
@@ -29,6 +29,7 @@ export async function createGroup(groupFormValues: GroupFormValues) {
 export async function createExpense(
   expenseFormValues: ExpenseFormValues,
   groupId: string,
+  participantId?: string,
 ): Promise<Expense> {
   const group = await getGroup(groupId)
   if (!group) throw new Error(`Invalid group ID: ${groupId}`)
@@ -41,9 +42,16 @@ export async function createExpense(
       throw new Error(`Invalid participant ID: ${participant}`)
   }
 
+  const expenseId = randomId()
+  await logActivity(groupId, ActivityType.CREATE_EXPENSE, {
+    participantId,
+    expenseId,
+    data: expenseFormValues.title,
+  })
+
   return prisma.expense.create({
     data: {
-      id: randomId(),
+      id: expenseId,
       groupId,
       expenseDate: expenseFormValues.expenseDate,
       categoryId: expenseFormValues.category,
@@ -75,7 +83,18 @@ export async function createExpense(
   })
 }
 
-export async function deleteExpense(expenseId: string) {
+export async function deleteExpense(
+  groupId: string,
+  expenseId: string,
+  participantId?: string,
+) {
+  const existingExpense = await getExpense(groupId, expenseId)
+  await logActivity(groupId, ActivityType.DELETE_EXPENSE, {
+    participantId,
+    expenseId,
+    data: existingExpense?.title,
+  })
+
   await prisma.expense.delete({
     where: { id: expenseId },
     include: { paidFor: true, paidBy: true },
@@ -110,6 +129,7 @@ export async function updateExpense(
   groupId: string,
   expenseId: string,
   expenseFormValues: ExpenseFormValues,
+  participantId?: string,
 ) {
   const group = await getGroup(groupId)
   if (!group) throw new Error(`Invalid group ID: ${groupId}`)
@@ -125,6 +145,12 @@ export async function updateExpense(
       throw new Error(`Invalid participant ID: ${participant}`)
   }
 
+  await logActivity(groupId, ActivityType.UPDATE_EXPENSE, {
+    participantId,
+    expenseId,
+    data: expenseFormValues.title,
+  })
+
   return prisma.expense.update({
     where: { id: expenseId },
     data: {
@@ -189,10 +215,13 @@ export async function updateExpense(
 export async function updateGroup(
   groupId: string,
   groupFormValues: GroupFormValues,
+  participantId?: string,
 ) {
   const existingGroup = await getGroup(groupId)
   if (!existingGroup) throw new Error('Invalid group ID')
 
+  await logActivity(groupId, ActivityType.UPDATE_GROUP, { participantId })
+
   return prisma.group.update({
     where: { id: groupId },
     data: {
@@ -273,3 +302,25 @@ export async function getExpense(groupId: string, expenseId: string) {
     include: { paidBy: true, paidFor: true, category: true, documents: true },
   })
 }
+
+export async function getActivities(groupId: string) {
+  return prisma.activity.findMany({
+    where: { groupId },
+    orderBy: [{ time: 'desc' }],
+  })
+}
+
+export async function logActivity(
+  groupId: string,
+  activityType: ActivityType,
+  extra?: { participantId?: string; expenseId?: string; data?: string },
+) {
+  return prisma.activity.create({
+    data: {
+      id: randomId(),
+      groupId,
+      activityType,
+      ...extra,
+    },
+  })
+}
diff --git a/src/lib/utils.ts b/src/lib/utils.ts
index 06d1989..4158166 100644
--- a/src/lib/utils.ts
+++ b/src/lib/utils.ts
@@ -10,9 +10,15 @@ export function delay(ms: number) {
   return new Promise((resolve) => setTimeout(resolve, ms))
 }
 
-export function formatExpenseDate(date: Date) {
-  return date.toLocaleDateString('en-US', {
-    dateStyle: 'medium',
+export type DateTimeStyle = NonNullable<
+  ConstructorParameters<typeof Intl.DateTimeFormat>[1]
+>['dateStyle']
+export function formatDate(
+  date: Date,
+  options: { dateStyle?: DateTimeStyle; timeStyle?: DateTimeStyle } = {},
+) {
+  return date.toLocaleString('en-GB', {
+    ...options,
     timeZone: 'UTC',
   })
 }