diff --git a/backend/package.json b/backend/package.json
index 7ec1ba5..715cf0f 100644
--- a/backend/package.json
+++ b/backend/package.json
@@ -26,6 +26,7 @@
     "@nestjs/core": "^8.0.0",
     "@nestjs/passport": "^8.2.1",
     "@nestjs/platform-express": "^8.4.5",
+    "cache-manager": "^4.1.0",
     "class-transformer": "^0.5.1",
     "dayjs": "^1.11.2",
     "express": "^4.18.1",
@@ -42,6 +43,7 @@
     "@nestjs/cli": "^8.0.0",
     "@nestjs/schematics": "^8.0.0",
     "@nestjs/testing": "^8.4.5",
+    "@types/cache-manager": "^4.0.1",
     "@types/express": "^4.17.13",
     "@types/jest": "27.5.0",
     "@types/node": "^16.0.0",
diff --git a/backend/src/app.module.ts b/backend/src/app.module.ts
index ea143c0..3f6d69a 100644
--- a/backend/src/app.module.ts
+++ b/backend/src/app.module.ts
@@ -1,4 +1,4 @@
-import { Module } from '@nestjs/common';
+import { CacheModule, Module } from '@nestjs/common';
 import { ConfigModule, ConfigService } from '@nestjs/config';
 import { FirebaseAuthStrategy } from './firebase/firebase-auth.strategy';
 import { FirestoreModule } from './firestore/firestore.module';
@@ -19,6 +19,7 @@ import { UsersModule } from './users/users.module';
       }),
       inject: [ConfigService],
     }),
+    CacheModule.register(),
     PostsModule,
     UsersModule,
   ],
diff --git a/backend/src/posts/posts.controller.spec.ts b/backend/src/posts/posts.controller.spec.ts
index a622054..c46e5e4 100644
--- a/backend/src/posts/posts.controller.spec.ts
+++ b/backend/src/posts/posts.controller.spec.ts
@@ -1,5 +1,6 @@
 import { PostsController } from './posts.controller';
 import { PostsService } from './posts.service';
+import { Cache } from 'cache-manager';
 
 jest.mock('./utils', () => {
   return {
@@ -13,12 +14,26 @@ jest.mock('./utils', () => {
 describe('PostsController', () => {
   let c: PostsController;
   let s: PostsService;
+  let cache: Cache;
   let old_env;
 
   beforeEach(() => {
     const collection = null;
     s = new PostsService(collection);
-    c = new PostsController(s);
+    cache = {
+      get: jest.fn(),
+      set: jest.fn(),
+      wrap: jest.fn(),
+      del: jest.fn(),
+      reset: jest.fn(),
+      store: {
+        get: jest.fn(),
+        set: jest.fn(),
+      },
+    };
+    jest.spyOn(cache, 'get').mockResolvedValue(null); // cache fails
+    jest.spyOn(cache, 'set');
+    c = new PostsController(s, cache);
     old_env = process.env;
     process.env = { MAX_NUMBER_POSTS_PER_DAY: '5', MAX_MESSAGE_LENGTH: '100' };
     jest.spyOn(s, 'countAllforUserByDate').mockResolvedValue(0);
diff --git a/backend/src/posts/posts.controller.ts b/backend/src/posts/posts.controller.ts
index 8709e64..d395d82 100644
--- a/backend/src/posts/posts.controller.ts
+++ b/backend/src/posts/posts.controller.ts
@@ -1,9 +1,11 @@
 import {
   BadRequestException,
   Body,
+  CACHE_MANAGER,
   Controller,
   Get,
   HttpCode,
+  Inject,
   Param,
   ParseIntPipe,
   Post,
@@ -21,10 +23,24 @@ import {
 import { PostsService } from './posts.service';
 import { FirebaseAuthGuard } from '../firebase/firebase-auth.guard';
 import { getDisplayNameByUserId } from './utils';
+import { Cache } from 'cache-manager';
 
 @Controller('posts')
 export class PostsController {
-  constructor(private readonly service: PostsService) {}
+  constructor(
+    private readonly service: PostsService,
+    @Inject(CACHE_MANAGER) private cacheManager: Cache,
+  ) {}
+
+  private async resolveUserName(userId: string): Promise<string> {
+    const key = `username-${userId}`;
+    let userName: string = await this.cacheManager.get(key);
+    if (userName === null) {
+      userName = await getDisplayNameByUserId(userId);
+      await this.cacheManager.set(key, userName);
+    }
+    return userName;
+  }
 
   @Get()
   @UseGuards(FirebaseAuthGuard)
@@ -49,7 +65,7 @@ export class PostsController {
         ...parentPost,
         likes: (parentPost.likes || []).length,
         likedByMe: (parentPost.likes || []).includes(userId),
-        userName: await getDisplayNameByUserId(parentPost.userId),
+        userName: await this.resolveUserName(parentPost.userId),
         comments: await this.service.countAllForParentId(parentPost.id),
       });
     }
@@ -58,7 +74,7 @@ export class PostsController {
         ...results[p],
         likes: (results[p].likes || []).length,
         likedByMe: (results[p].likes || []).includes(userId),
-        userName: await getDisplayNameByUserId(results[p].userId),
+        userName: await this.resolveUserName(results[p].userId),
         comments: await this.service.countAllForParentId(results[p].id),
       });
     }
@@ -194,7 +210,7 @@ export class PostsController {
 
     const post = await this.service.get(id);
 
-    const userName = await getDisplayNameByUserId(post.userId);
+    const userName = await this.resolveUserName(post.userId);
     const comments = post.parentId
       ? await this.service.countAllForParentId(post.parentId)
       : 0;
diff --git a/backend/yarn.lock b/backend/yarn.lock
index 1f18fe2..4caf608 100644
--- a/backend/yarn.lock
+++ b/backend/yarn.lock
@@ -1052,6 +1052,11 @@
     "@types/connect" "*"
     "@types/node" "*"
 
+"@types/cache-manager@^4.0.1":
+  version "4.0.1"
+  resolved "https://registry.yarnpkg.com/@types/cache-manager/-/cache-manager-4.0.1.tgz#96107bfc3d35100fc6b65fd9b0ea0bcc4ff5118c"
+  integrity sha512-w4Gm7qg4ohvk0k4CLhOoqnMohWEyeyAOTovPgkguhuDCfVEV1wN/HWEd1XzB1S9/NV9pUcZcc498qU4E15ck6A==
+
 "@types/connect@*":
   version "3.4.35"
   resolved "https://registry.yarnpkg.com/@types/connect/-/connect-3.4.35.tgz#5fcf6ae445e4021d1fc2219a4873cc73a3bb2ad1"
@@ -1637,6 +1642,11 @@ async-retry@^1.3.3:
   dependencies:
     retry "0.13.1"
 
+async@3.2.3:
+  version "3.2.3"
+  resolved "https://registry.yarnpkg.com/async/-/async-3.2.3.tgz#ac53dafd3f4720ee9e8a160628f18ea91df196c9"
+  integrity sha512-spZRyzKL5l5BZQrr/6m/SqFdBN0q3OCI0f9rjfBzCMBIP4p75P620rR3gTmaksNOhmzgdxcaxdNfMy6anrbM0g==
+
 asynckit@^0.4.0:
   version "0.4.0"
   resolved "https://registry.yarnpkg.com/asynckit/-/asynckit-0.4.0.tgz#c79ed97f7f34cb8f2ba1bc9790bcc366474b4b79"
@@ -1828,6 +1838,15 @@ bytes@3.1.2:
   resolved "https://registry.yarnpkg.com/bytes/-/bytes-3.1.2.tgz#8b0beeb98605adf1b128fa4386403c009e0221a5"
   integrity sha512-/Nf7TyzTx6S3yRJObOAV7956r8cr2+Oj8AC5dt8wSP3BQAoeX58NoHyCU8P8zGkNXStjTSi6fzO6F0pBdcYbEg==
 
+cache-manager@^4.1.0:
+  version "4.1.0"
+  resolved "https://registry.yarnpkg.com/cache-manager/-/cache-manager-4.1.0.tgz#aa986421f1c975a862d6de88edb9ab1d30f4bd39"
+  integrity sha512-ZGM6dLxrP65bfOZmcviWMadUOCICqpLs92+P/S5tj8onz+k+tB7Gr+SAgOUHCQtfm2gYEQDHiKeul4+tYPOJ8A==
+  dependencies:
+    async "3.2.3"
+    lodash.clonedeep "^4.5.0"
+    lru-cache "^7.10.1"
+
 call-bind@^1.0.0:
   version "1.0.2"
   resolved "https://registry.yarnpkg.com/call-bind/-/call-bind-1.0.2.tgz#b1d4e89e688119c3c9a903ad30abb2f6a919be3c"
@@ -3984,6 +4003,11 @@ lru-cache@^6.0.0:
   dependencies:
     yallist "^4.0.0"
 
+lru-cache@^7.10.1:
+  version "7.14.0"
+  resolved "https://registry.yarnpkg.com/lru-cache/-/lru-cache-7.14.0.tgz#21be64954a4680e303a09e9468f880b98a0b3c7f"
+  integrity sha512-EIRtP1GrSJny0dqb50QXRUNBxHJhcpxHC++M5tD7RYbvLLn5KVWKsbyswSSqDuU15UFi3bgTQIY8nhDMeF6aDQ==
+
 lru-cache@~4.0.0:
   version "4.0.2"
   resolved "https://registry.yarnpkg.com/lru-cache/-/lru-cache-4.0.2.tgz#1d17679c069cda5d040991a09dbc2c0db377e55e"