diff --git a/src/repositories/mongo-card-repository.ts b/src/repositories/mongo-card-repository.ts
new file mode 100644
index 0000000..4f7f29c
--- /dev/null
+++ b/src/repositories/mongo-card-repository.ts
@@ -0,0 +1,126 @@
+import { MongoClient, type Collection } from 'mongodb'
+import type { Card, CardInput } from '../domain/card'
+import type { CardRepository } from '../domain/card-repository'
+
+interface CardDocument {
+  c_id: string
+  question: string
+  response: string
+  theme: string
+  tags: string[]
+  createdAt: Date
+  updatedAt: Date
+}
+
+const DOC_FIELDS = {
+  _id: 0,
+  c_id: 1,
+  question: 1,
+  response: 1,
+  theme: 1,
+  tags: 1,
+  createdAt: 1,
+  updatedAt: 1,
+}
+
+export class MongoCardRepository implements CardRepository {
+  private readonly collection: Collection<CardDocument>
+
+  constructor(collection?: Collection<CardDocument>) {
+    if (collection) {
+      this.collection = collection
+    } else {
+      const client = new MongoClient(
+        process.env.MONGODB_URI ?? 'mongodb://flashcards:flashcards@localhost:127017/flashcards',
+      )
+      this.collection = client
+        .db(process.env.MONGODB_DATABASE ?? 'flashcards')
+        .collection<CardDocument>('cards')
+    }
+  }
+
+  private mapDoc(doc: CardDocument): Card {
+    return {
+      id: doc.c_id,
+      question: doc.question,
+      response: doc.response,
+      theme: doc.theme,
+      tags: doc.tags,
+      createdAt: doc.createdAt,
+      updatedAt: doc.updatedAt,
+    }
+  }
+
+  async findAll(): Promise<Card[]> {
+    const docs = await this.collection.find({}, { projection: DOC_FIELDS }).toArray()
+    return docs.map((doc) => this.mapDoc(doc))
+  }
+
+  async findById(id: string): Promise<Card | null> {
+    const doc = await this.collection.findOne({ c_id: id }, { projection: DOC_FIELDS })
+    return doc ? this.mapDoc(doc) : null
+  }
+
+  async create(input: CardInput): Promise<Card> {
+    const doc: CardDocument = {
+      c_id: crypto.randomUUID(),
+      question: input.question,
+      response: input.response,
+      theme: input.theme,
+      tags: input.tags ?? [],
+      createdAt: new Date(),
+      updatedAt: new Date(),
+    }
+    await this.collection.insertOne(doc)
+    return this.mapDoc(doc)
+  }
+
+  async update(id: string, input: Partial<CardInput>): Promise<Card | null> {
+    const set: Partial<CardDocument> = { updatedAt: new Date() }
+    if (input.question !== undefined) {
+      set.question = input.question
+    }
+    if (input.response !== undefined) {
+      set.response = input.response
+    }
+    if (input.theme !== undefined) {
+      set.theme = input.theme
+    }
+    if (input.tags !== undefined) {
+      set.tags = input.tags
+    }
+    const result = await this.collection.updateOne({ c_id: id }, { $set: set })
+    if (result.matchedCount === 0) {
+      return null
+    }
+    return this.findById(id)
+  }
+
+  async delete(id: string): Promise<boolean> {
+    const result = await this.collection.deleteOne({ c_id: id })
+    return result.deletedCount > 0
+  }
+
+  async findRandom(): Promise<Card | null> {
+    const docs = await this.collection
+      .aggregate<CardDocument>([{ $sample: { size: 1 } }, { $project: DOC_FIELDS }])
+      .toArray()
+    return docs[0] ? this.mapDoc(docs[0]) : null
+  }
+
+  async findRandomByTheme(theme: string): Promise<Card | null> {
+    const docs = await this.collection
+      .aggregate<CardDocument>([
+        { $match: { theme } },
+        { $sample: { size: 1 } },
+        { $project: DOC_FIELDS },
+      ])
+      .toArray()
+    return docs[0] ? this.mapDoc(docs[0]) : null
+  }
+
+  async findThemes(): Promise<string[]> {
+    const themes: string[] = await this.collection.distinct('theme')
+    return themes.sort()
+  }
+}
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