diff --git a/CHANGELOG.md b/CHANGELOG.md
index 0c06b1d..8202cb4 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -6,6 +6,9 @@ All notable changes to `doc` are documented here.
 
 ### Fixed
 
+- Persist like identity per viewer using a server-side `PubDocLike` table and cookie-based
+  anonymous viewer token. Duplicate likes from the same viewer are now idempotent, cancel
+  only succeeds if that viewer holds a like, and counts survive reload across devices.
 - Add an in-app back button to the TopBar that appears only after the first in-app navigation,
   and scope the entry-document flag to `sessionStorage` so it survives SPA navigation but resets
   on full page reload (#66).
diff --git a/prisma/migrations/20260918000000_add_pub_doc_like/migration.sql b/prisma/migrations/20260918000000_add_pub_doc_like/migration.sql
new file mode 100644
index 0000000..fa447d0
--- /dev/null
+++ b/prisma/migrations/20260918000000_add_pub_doc_like/migration.sql
@@ -0,0 +1,18 @@
+-- CreateTable
+CREATE TABLE "PubDocLike" (
+    "id" TEXT NOT NULL,
+    "viewerId" TEXT NOT NULL,
+    "pubDocId" TEXT NOT NULL,
+    "createdAt" TIMESTAMP(3) NOT NULL DEFAULT CURRENT_TIMESTAMP,
+
+    CONSTRAINT "PubDocLike_pkey" PRIMARY KEY ("id")
+);
+
+-- CreateIndex
+CREATE INDEX "PubDocLike_pubDocId_idx" ON "PubDocLike"("pubDocId");
+
+-- CreateIndex
+CREATE UNIQUE INDEX "PubDocLike_viewerId_pubDocId_key" ON "PubDocLike"("viewerId", "pubDocId");
+
+-- AddForeignKey
+ALTER TABLE "PubDocLike" ADD CONSTRAINT "PubDocLike_pubDocId_fkey" FOREIGN KEY ("pubDocId") REFERENCES "PubDoc"("id") ON DELETE CASCADE ON UPDATE CASCADE;
diff --git a/prisma/schema.prisma b/prisma/schema.prisma
index af21a3a..b2e8029 100644
--- a/prisma/schema.prisma
+++ b/prisma/schema.prisma
@@ -200,6 +200,19 @@ model PubDoc {
   user            User         @relation(fields: [userId], references: [id], name: "pubDocs")
   doc             Doc          @relation(fields: [docId], references: [id], onDelete: Cascade)
   thumbUpCount    Int          @default(0)
+  likes           PubDocLike[]
+}
+
+model PubDocLike {
+  id        String   @id @default(cuid())
+  viewerId  String
+  pubDocId  String
+  createdAt DateTime @default(now())
+
+  pubDoc PubDoc @relation(fields: [pubDocId], references: [id], onDelete: Cascade)
+
+  @@unique([viewerId, pubDocId])
+  @@index([pubDocId])
 }
 
 model AuditLog {
diff --git a/src/__tests__/api/pub-like-viewer.test.ts b/src/__tests__/api/pub-like-viewer.test.ts
new file mode 100644
index 0000000..7ce4482
--- /dev/null
+++ b/src/__tests__/api/pub-like-viewer.test.ts
@@ -0,0 +1,134 @@
+import { beforeEach, describe, expect, it, vi } from 'vitest'
+
+const mocks = vi.hoisted(() => ({
+  resolveViewerId: vi.fn(),
+  pubFindUnique: vi.fn(),
+  likeFindUnique: vi.fn(),
+  likeCreate: vi.fn(),
+  likeDeleteMany: vi.fn(),
+  pubUpdate: vi.fn(),
+  pubUpdateMany: vi.fn(),
+  transaction: vi.fn(),
+}))
+
+vi.mock('server-only', () => ({}))
+vi.mock('@/lib/viewer-id', () => ({ resolveViewerId: mocks.resolveViewerId }))
+vi.mock('@/db/db', () => ({
+  db: {
+    pubDoc: {
+      findUnique: mocks.pubFindUnique,
+      update: mocks.pubUpdate,
+      updateMany: mocks.pubUpdateMany,
+    },
+    pubDocLike: {
+      findUnique: mocks.likeFindUnique,
+      create: mocks.likeCreate,
+      deleteMany: mocks.likeDeleteMany,
+    },
+    $transaction: mocks.transaction,
+  },
+}))
+
+import { GET, PATCH as increase } from '@/app/api/pub/thumb-up/[publishId]/route'
+import { PATCH as decrease } from '@/app/api/pub/thumb-up-decrease/[publishId]/route'
+
+const params = { publishId: 'pub-1' }
+const request = new Request('http://doc.test/api/pub/thumb-up/pub-1', { method: 'PATCH' })
+
+describe('published like GET/PATCH', () => {
+  beforeEach(() => {
+    Object.values(mocks).forEach((mock) => mock.mockReset())
+    mocks.resolveViewerId.mockResolvedValue({ viewerId: 'anon-1', setCookie: false })
+    mocks.transaction.mockImplementation(async (fn: (tx: unknown) => unknown) =>
+      fn({
+        pubDoc: {
+          findUnique: mocks.pubFindUnique,
+          update: mocks.pubUpdate,
+          updateMany: mocks.pubUpdateMany,
+        },
+        pubDocLike: {
+          create: mocks.likeCreate,
+          deleteMany: mocks.likeDeleteMany,
+        },
+      })
+    )
+  })
+
+  it('GET reports whether this viewer currently holds a like', async () => {
+    mocks.pubFindUnique.mockResolvedValue({ id: 'doc-pub', thumbUpCount: 3 })
+    mocks.likeFindUnique.mockResolvedValue({ id: 'like-1' })
+
+    const response = await GET(request, { params })
+    await expect(response.json()).resolves.toEqual({
+      errno: 0,
+      data: { liked: true, count: 3 },
+    })
+  })
+
+  it('PATCH increase creates the like row before incrementing', async () => {
+    mocks.pubFindUnique.mockResolvedValue({ id: 'doc-pub', thumbUpCount: 0 })
+    mocks.likeCreate.mockResolvedValue({ id: 'like-1' })
+    mocks.pubUpdate.mockResolvedValue({ thumbUpCount: 1 })
+
+    const response = await increase(request, { params })
+    await expect(response.json()).resolves.toEqual({
+      errno: 0,
+      data: { liked: true, count: 1 },
+    })
+    expect(mocks.likeCreate).toHaveBeenCalledWith({
+      data: { viewerId: 'anon-1', pubDocId: 'doc-pub' },
+    })
+    expect(mocks.pubUpdate).toHaveBeenCalledWith({
+      where: { publishId: 'pub-1' },
+      data: { thumbUpCount: { increment: 1 } },
+      select: { thumbUpCount: true },
+    })
+  })
+
+  it('PATCH increase is idempotent when create hits the unique constraint', async () => {
+    mocks.pubFindUnique
+      .mockResolvedValueOnce({ id: 'doc-pub', thumbUpCount: 1 })
+      .mockResolvedValueOnce({ id: 'doc-pub', thumbUpCount: 1 })
+    mocks.likeCreate.mockRejectedValue({ code: 'P2002' })
+
+    const response = await increase(request, { params })
+    await expect(response.json()).resolves.toEqual({
+      errno: 0,
+      data: { liked: true, count: 1 },
+    })
+    expect(mocks.pubUpdate).not.toHaveBeenCalled()
+  })
+
+  it('PATCH decrease deletes and decrements in one transaction', async () => {
+    mocks.pubFindUnique
+      .mockResolvedValueOnce({ id: 'doc-pub', thumbUpCount: 2 })
+      .mockResolvedValueOnce({ id: 'doc-pub', thumbUpCount: 1 })
+    mocks.likeDeleteMany.mockResolvedValue({ count: 1 })
+    mocks.pubUpdateMany.mockResolvedValue({ count: 1 })
+
+    const response = await decrease(request, { params })
+    await expect(response.json()).resolves.toEqual({
+      errno: 0,
+      data: { liked: false, count: 1 },
+    })
+    expect(mocks.likeDeleteMany).toHaveBeenCalledWith({
+      where: { viewerId: 'anon-1', pubDocId: 'doc-pub' },
+    })
+    expect(mocks.pubUpdateMany).toHaveBeenCalledWith({
+      where: { publishId: 'pub-1', thumbUpCount: { gt: 0 } },
+      data: { thumbUpCount: { decrement: 1 } },
+    })
+  })
+
+  it('PATCH decrease does not decrement when this viewer has no like', async () => {
+    mocks.pubFindUnique.mockResolvedValue({ id: 'doc-pub', thumbUpCount: 2 })
+    mocks.likeDeleteMany.mockResolvedValue({ count: 0 })
+
+    const response = await decrease(request, { params })
+    await expect(response.json()).resolves.toEqual({
+      errno: 0,
+      data: { liked: false, count: 2 },
+    })
+    expect(mocks.pubUpdateMany).not.toHaveBeenCalled()
+  })
+})
diff --git a/src/app/api/pub/thumb-up-decrease/[publishId]/route.ts b/src/app/api/pub/thumb-up-decrease/[publishId]/route.ts
index 8be9b83..65298da 100644
--- a/src/app/api/pub/thumb-up-decrease/[publishId]/route.ts
+++ b/src/app/api/pub/thumb-up-decrease/[publishId]/route.ts
@@ -1,23 +1,33 @@
 import { db } from '@/db/db'
 import { genSuccessData, genErrorData } from '@/app/api/utils/gen-res-data'
+import { resolveViewerId } from '@/lib/viewer-id'
 
-export async function PATCH(request: Request, { params }: { params: { publishId: string } }) {
-  const { publishId } = params // `publishId` is publish url suffix
-  return Response.json(genSuccessData())
+export async function PATCH(_request: Request, { params }: { params: { publishId: string } }) {
+  const { publishId } = params
 
-  // try {
-  //   const p = await db.pubDoc.update({
-  //     where: {
-  //       publishId,
-  //     },
-  //     data: {
-  //       thumbUpCount: {
-  //         decrement: 1, // Decrement the thumb up count by 1
-  //       },
-  //     },
-  //   })
-  //   return Response.json(genSuccessData(p))
-  // } catch (ex: any) {
-  //   return Response.json(genErrorData(ex.message))
-  // }
+  try {
+    const { viewerId } = await resolveViewerId()
+    const pubDoc = await db.pubDoc.findUnique({ where: { publishId }, select: { id: true, thumbUpCount: true } })
+    if (!pubDoc) return Response.json(genErrorData('not found'))
+
+    const result = await db.$transaction(async (tx) => {
+      const deleted = await tx.pubDocLike.deleteMany({
+        where: { viewerId, pubDocId: pubDoc.id },
+      })
+      if (deleted.count === 0) {
+        const current = await tx.pubDoc.findUnique({ where: { publishId }, select: { thumbUpCount: true } })
+        return { liked: false as const, count: current?.thumbUpCount ?? pubDoc.thumbUpCount }
+      }
+      await tx.pubDoc.updateMany({
+        where: { publishId, thumbUpCount: { gt: 0 } },
+        data: { thumbUpCount: { decrement: 1 } },
+      })
+      const current = await tx.pubDoc.findUnique({ where: { publishId }, select: { thumbUpCount: true } })
+      return { liked: false as const, count: current?.thumbUpCount ?? 0 }
+    })
+
+    return Response.json(genSuccessData(result))
+  } catch (ex: any) {
+    return Response.json(genErrorData(ex.message))
+  }
 }
diff --git a/src/app/api/pub/thumb-up/[publishId]/route.ts b/src/app/api/pub/thumb-up/[publishId]/route.ts
index d3b4441..8ecefd5 100644
--- a/src/app/api/pub/thumb-up/[publishId]/route.ts
+++ b/src/app/api/pub/thumb-up/[publishId]/route.ts
@@ -1,21 +1,54 @@
 import { db } from '@/db/db'
 import { genSuccessData, genErrorData } from '@/app/api/utils/gen-res-data'
+import { resolveViewerId } from '@/lib/viewer-id'
 
-export async function PATCH(request: Request, { params }: { params: { publishId: string } }) {
-  const { publishId } = params // `publishId` is publish url suffix
+function isUniqueViolation(error: unknown): boolean {
+  return typeof error === 'object' && error !== null && 'code' in error && (error as { code: unknown }).code === 'P2002'
+}
+
+export async function GET(_request: Request, { params }: { params: { publishId: string } }) {
+  const { publishId } = params
 
   try {
-    const p = await db.pubDoc.update({
-      where: {
-        publishId,
-      },
-      data: {
-        thumbUpCount: {
-          increment: 1, // Increment the thumb up count by 1
-        },
-      },
+    const { viewerId } = await resolveViewerId()
+    const pubDoc = await db.pubDoc.findUnique({ where: { publishId }, select: { id: true, thumbUpCount: true } })
+    if (!pubDoc) return Response.json(genErrorData('not found'))
+
+    const like = await db.pubDocLike.findUnique({
+      where: { viewerId_pubDocId: { viewerId, pubDocId: pubDoc.id } },
     })
-    return Response.json(genSuccessData(p))
+
+    return Response.json(genSuccessData({ liked: !!like, count: pubDoc.thumbUpCount }))
+  } catch (ex: any) {
+    return Response.json(genErrorData(ex.message))
+  }
+}
+
+export async function PATCH(_request: Request, { params }: { params: { publishId: string } }) {
+  const { publishId } = params
+
+  try {
+    const { viewerId } = await resolveViewerId()
+    const pubDoc = await db.pubDoc.findUnique({ where: { publishId }, select: { id: true, thumbUpCount: true } })
+    if (!pubDoc) return Response.json(genErrorData('not found'))
+
+    try {
+      const updated = await db.$transaction(async (tx) => {
+        await tx.pubDocLike.create({
+          data: { viewerId, pubDocId: pubDoc.id },
+        })
+        return tx.pubDoc.update({
+          where: { publishId },
+          data: { thumbUpCount: { increment: 1 } },
+          select: { thumbUpCount: true },
+        })
+      })
+      return Response.json(genSuccessData({ liked: true, count: updated.thumbUpCount }))
+    } catch (error) {
+      if (!isUniqueViolation(error)) throw error
+      const current = await db.pubDoc.findUnique({ where: { publishId }, select: { thumbUpCount: true } })
+      return Response.json(genSuccessData({ liked: true, count: current?.thumbUpCount ?? pubDoc.thumbUpCount }))
+    }
   } catch (ex: any) {
     return Response.json(genErrorData(ex.message))
   }
diff --git a/src/components/thumb-up-button.tsx b/src/components/thumb-up-button.tsx
index 937f229..f887d4a 100644
--- a/src/components/thumb-up-button.tsx
+++ b/src/components/thumb-up-button.tsx
@@ -1,53 +1,56 @@
 'use client'
 
-import { useState, useEffect, useMemo } from 'react'
+import { useState, useEffect } from 'react'
 import { ThumbsUp } from 'lucide-react'
 import { Button } from '@/components/ui/button'
-import { patch } from '@/lib/ajax'
+import { get, patch } from '@/lib/ajax'
 
 export default function ThumbUpButton(props: { initialCount: number; publishId: string }) {
-  const { initialCount, publishId } = props // Default count if not provided
-  const STORE_KEY = useMemo(() => `thumbUp-${publishId}`, [publishId])
+  const { initialCount, publishId } = props
 
   const [loading, setLoading] = useState(true)
   const [isLiked, setIsLiked] = useState(false)
+  const [thumbUpCount, setThumbUpCount] = useState(initialCount || 0)
+
   useEffect(() => {
-    // Check if the user has already liked this publishId
-    const liked = localStorage.getItem(STORE_KEY)
-    if (liked) {
-      setIsLiked(true)
-    }
-    setLoading(false)
-  }, [STORE_KEY])
+    get(`/api/pub/thumb-up/${publishId}`)
+      .then((res) => {
+        if (res.errno === 0 && res.data) {
+          setIsLiked(res.data.liked)
+          setThumbUpCount(res.data.count)
+        }
+      })
+      .catch(() => {})
+      .finally(() => setLoading(false))
+  }, [publishId])
 
-  const [thumbUpCount, setThumbUpCount] = useState(initialCount || 0)
   const handleThumbUp = async () => {
-    if (loading) return // Prevent multiple clicks
+    if (loading) return
+    const prevLiked = isLiked
+    const prevCount = thumbUpCount
+
     if (isLiked) {
-      if (thumbUpCount <= 0) return // Prevent decrementing below zero
-      setThumbUpCount(thumbUpCount - 1)
       setIsLiked(false)
-      localStorage.removeItem(STORE_KEY) // Remove publishId from localStorage
-      await patchData(`/api/pub/thumb-up-decrease/${publishId}`) // Decrease thumb up count in the backend
+      setThumbUpCount(Math.max(0, thumbUpCount - 1))
     } else {
-      setThumbUpCount(thumbUpCount + 1)
       setIsLiked(true)
-      localStorage.setItem(STORE_KEY, 'true') // store publishId in localStorage
-      await patchData(`/api/pub/thumb-up/${publishId}`) // Increase thumb up count in the backend
+      setThumbUpCount(thumbUpCount + 1)
     }
-  }
 
-  async function patchData(url: string) {
     setLoading(true)
     try {
-      const response = await patch(url, {})
-      if (response.errno !== 0) {
-        throw new Error('Network response was not ok')
+      const url = isLiked ? `/api/pub/thumb-up-decrease/${publishId}` : `/api/pub/thumb-up/${publishId}`
+      const res = await patch(url, {})
+      if (res.errno === 0 && res.data) {
+        setIsLiked(res.data.liked)
+        setThumbUpCount(res.data.count)
+      } else {
+        setIsLiked(prevLiked)
+        setThumbUpCount(prevCount)
       }
-      const data = response.data
-      return data
-    } catch (error) {
-      console.error('Error:', error)
+    } catch {
+      setIsLiked(prevLiked)
+      setThumbUpCount(prevCount)
     } finally {
       setLoading(false)
     }
diff --git a/src/lib/viewer-id.ts b/src/lib/viewer-id.ts
new file mode 100644
index 0000000..e235364
--- /dev/null
+++ b/src/lib/viewer-id.ts
@@ -0,0 +1,35 @@
+import 'server-only'
+import { cookies } from 'next/headers'
+import { auth } from 'auth'
+
+const COOKIE_NAME = 'viewer_id'
+const COOKIE_MAX_AGE = 60 * 60 * 24 * 365
+
+/**
+ * Viewer identity for published-document likes (#72).
+ * Signed-in users are `user:{id}`. Anonymous visitors get an httpOnly UUID
+ * cookie: it is a documented opaque token, not a signed capability, and it
+ * only scopes like rows for this browser profile.
+ */
+export async function resolveViewerId(): Promise<{ viewerId: string; setCookie: boolean }> {
+  const session = await auth()
+  if (session?.user?.id) {
+    return { viewerId: `user:${session.user.id}`, setCookie: false }
+  }
+
+  const cookieStore = await cookies()
+  const existing = cookieStore.get(COOKIE_NAME)
+  if (existing?.value) {
+    return { viewerId: existing.value, setCookie: false }
+  }
+
+  const viewerId = crypto.randomUUID()
+  cookieStore.set(COOKIE_NAME, viewerId, {
+    httpOnly: true,
+    sameSite: 'lax',
+    secure: process.env.NODE_ENV === 'production',
+    maxAge: COOKIE_MAX_AGE,
+    path: '/',
+  })
+  return { viewerId, setCookie: true }
+}