diff --git a/src/db/schema.ts b/src/db/schema.ts
index 6d1cc3e..b51bdb2 100644
--- a/src/db/schema.ts
+++ b/src/db/schema.ts
@@ -28,6 +28,41 @@ export const items = sqliteTable("items", {
     .$defaultFn(() => new Date()),
 });
 
+export const threads = sqliteTable("threads", {
+  id: integer("id").primaryKey({ autoIncrement: true }),
+  name: text("name").notNull(),
+  status: text("status").notNull().default("active"),
+  resolvedCandidateId: integer("resolved_candidate_id"),
+  createdAt: integer("created_at", { mode: "timestamp" })
+    .notNull()
+    .$defaultFn(() => new Date()),
+  updatedAt: integer("updated_at", { mode: "timestamp" })
+    .notNull()
+    .$defaultFn(() => new Date()),
+});
+
+export const threadCandidates = sqliteTable("thread_candidates", {
+  id: integer("id").primaryKey({ autoIncrement: true }),
+  threadId: integer("thread_id")
+    .notNull()
+    .references(() => threads.id, { onDelete: "cascade" }),
+  name: text("name").notNull(),
+  weightGrams: real("weight_grams"),
+  priceCents: integer("price_cents"),
+  categoryId: integer("category_id")
+    .notNull()
+    .references(() => categories.id),
+  notes: text("notes"),
+  productUrl: text("product_url"),
+  imageFilename: text("image_filename"),
+  createdAt: integer("created_at", { mode: "timestamp" })
+    .notNull()
+    .$defaultFn(() => new Date()),
+  updatedAt: integer("updated_at", { mode: "timestamp" })
+    .notNull()
+    .$defaultFn(() => new Date()),
+});
+
 export const settings = sqliteTable("settings", {
   key: text("key").primaryKey(),
   value: text("value").notNull(),
diff --git a/src/shared/schemas.ts b/src/shared/schemas.ts
index b1f2a82..eb2e2dc 100644
--- a/src/shared/schemas.ts
+++ b/src/shared/schemas.ts
@@ -23,3 +23,28 @@ export const updateCategorySchema = z.object({
   name: z.string().min(1).optional(),
   emoji: z.string().min(1).max(4).optional(),
 });
+
+// Thread schemas
+export const createThreadSchema = z.object({
+  name: z.string().min(1, "Thread name is required"),
+});
+
+export const updateThreadSchema = z.object({
+  name: z.string().min(1).optional(),
+});
+
+// Candidate schemas (same fields as items)
+export const createCandidateSchema = z.object({
+  name: z.string().min(1, "Name is required"),
+  weightGrams: z.number().nonnegative().optional(),
+  priceCents: z.number().int().nonnegative().optional(),
+  categoryId: z.number().int().positive(),
+  notes: z.string().optional(),
+  productUrl: z.string().url().optional().or(z.literal("")),
+});
+
+export const updateCandidateSchema = createCandidateSchema.partial();
+
+export const resolveThreadSchema = z.object({
+  candidateId: z.number().int().positive(),
+});
diff --git a/src/shared/types.ts b/src/shared/types.ts
index 91fe285..685fd6e 100644
--- a/src/shared/types.ts
+++ b/src/shared/types.ts
@@ -4,15 +4,27 @@ import type {
   updateItemSchema,
   createCategorySchema,
   updateCategorySchema,
+  createThreadSchema,
+  updateThreadSchema,
+  createCandidateSchema,
+  updateCandidateSchema,
+  resolveThreadSchema,
 } from "./schemas.ts";
-import type { items, categories } from "../db/schema.ts";
+import type { items, categories, threads, threadCandidates } from "../db/schema.ts";
 
 // Types inferred from Zod schemas
 export type CreateItem = z.infer<typeof createItemSchema>;
 export type UpdateItem = z.infer<typeof updateItemSchema>;
 export type CreateCategory = z.infer<typeof createCategorySchema>;
 export type UpdateCategory = z.infer<typeof updateCategorySchema>;
+export type CreateThread = z.infer<typeof createThreadSchema>;
+export type UpdateThread = z.infer<typeof updateThreadSchema>;
+export type CreateCandidate = z.infer<typeof createCandidateSchema>;
+export type UpdateCandidate = z.infer<typeof updateCandidateSchema>;
+export type ResolveThread = z.infer<typeof resolveThreadSchema>;
 
 // Types inferred from Drizzle schema
 export type Item = typeof items.$inferSelect;
 export type Category = typeof categories.$inferSelect;
+export type Thread = typeof threads.$inferSelect;
+export type ThreadCandidate = typeof threadCandidates.$inferSelect;
diff --git a/tests/helpers/db.ts b/tests/helpers/db.ts
index afb57a8..c7725f7 100644
--- a/tests/helpers/db.ts
+++ b/tests/helpers/db.ts
@@ -31,6 +31,33 @@ export function createTestDb() {
     )
   `);
 
+  sqlite.run(`
+    CREATE TABLE threads (
+      id INTEGER PRIMARY KEY AUTOINCREMENT,
+      name TEXT NOT NULL,
+      status TEXT NOT NULL DEFAULT 'active',
+      resolved_candidate_id INTEGER,
+      created_at INTEGER NOT NULL DEFAULT (unixepoch()),
+      updated_at INTEGER NOT NULL DEFAULT (unixepoch())
+    )
+  `);
+
+  sqlite.run(`
+    CREATE TABLE thread_candidates (
+      id INTEGER PRIMARY KEY AUTOINCREMENT,
+      thread_id INTEGER NOT NULL REFERENCES threads(id) ON DELETE CASCADE,
+      name TEXT NOT NULL,
+      weight_grams REAL,
+      price_cents INTEGER,
+      category_id INTEGER NOT NULL REFERENCES categories(id),
+      notes TEXT,
+      product_url TEXT,
+      image_filename TEXT,
+      created_at INTEGER NOT NULL DEFAULT (unixepoch()),
+      updated_at INTEGER NOT NULL DEFAULT (unixepoch())
+    )
+  `);
+
   sqlite.run(`
     CREATE TABLE settings (
       key TEXT PRIMARY KEY,
diff --git a/tests/services/thread.service.test.ts b/tests/services/thread.service.test.ts
new file mode 100644
index 0000000..6a19c6e
--- /dev/null
+++ b/tests/services/thread.service.test.ts
@@ -0,0 +1,280 @@
+import { describe, it, expect, beforeEach } from "bun:test";
+import { createTestDb } from "../helpers/db.ts";
+import {
+  createThread,
+  getAllThreads,
+  getThreadWithCandidates,
+  createCandidate,
+  updateCandidate,
+  deleteCandidate,
+  updateThread,
+  deleteThread,
+  resolveThread,
+} from "../../src/server/services/thread.service.ts";
+import { createItem } from "../../src/server/services/item.service.ts";
+
+describe("Thread Service", () => {
+  let db: ReturnType<typeof createTestDb>;
+
+  beforeEach(() => {
+    db = createTestDb();
+  });
+
+  describe("createThread", () => {
+    it("creates thread with name, returns thread with id/status/timestamps", () => {
+      const thread = createThread(db, { name: "New Tent" });
+
+      expect(thread).toBeDefined();
+      expect(thread.id).toBeGreaterThan(0);
+      expect(thread.name).toBe("New Tent");
+      expect(thread.status).toBe("active");
+      expect(thread.resolvedCandidateId).toBeNull();
+      expect(thread.createdAt).toBeDefined();
+      expect(thread.updatedAt).toBeDefined();
+    });
+  });
+
+  describe("getAllThreads", () => {
+    it("returns active threads with candidateCount and price range", () => {
+      const thread = createThread(db, { name: "Backpack Options" });
+      createCandidate(db, thread.id, {
+        name: "Pack A",
+        categoryId: 1,
+        priceCents: 20000,
+      });
+      createCandidate(db, thread.id, {
+        name: "Pack B",
+        categoryId: 1,
+        priceCents: 35000,
+      });
+
+      const threads = getAllThreads(db);
+      expect(threads).toHaveLength(1);
+      expect(threads[0].name).toBe("Backpack Options");
+      expect(threads[0].candidateCount).toBe(2);
+      expect(threads[0].minPriceCents).toBe(20000);
+      expect(threads[0].maxPriceCents).toBe(35000);
+    });
+
+    it("excludes resolved threads by default", () => {
+      const t1 = createThread(db, { name: "Active Thread" });
+      const t2 = createThread(db, { name: "Resolved Thread" });
+      const candidate = createCandidate(db, t2.id, {
+        name: "Winner",
+        categoryId: 1,
+      });
+      resolveThread(db, t2.id, candidate.id);
+
+      const active = getAllThreads(db);
+      expect(active).toHaveLength(1);
+      expect(active[0].name).toBe("Active Thread");
+    });
+
+    it("includes resolved threads when includeResolved=true", () => {
+      const t1 = createThread(db, { name: "Active Thread" });
+      const t2 = createThread(db, { name: "Resolved Thread" });
+      const candidate = createCandidate(db, t2.id, {
+        name: "Winner",
+        categoryId: 1,
+      });
+      resolveThread(db, t2.id, candidate.id);
+
+      const all = getAllThreads(db, true);
+      expect(all).toHaveLength(2);
+    });
+  });
+
+  describe("getThreadWithCandidates", () => {
+    it("returns thread with nested candidates array including category info", () => {
+      const thread = createThread(db, { name: "Tent Options" });
+      createCandidate(db, thread.id, {
+        name: "Tent A",
+        categoryId: 1,
+        weightGrams: 1200,
+        priceCents: 30000,
+      });
+
+      const result = getThreadWithCandidates(db, thread.id);
+      expect(result).toBeDefined();
+      expect(result!.name).toBe("Tent Options");
+      expect(result!.candidates).toHaveLength(1);
+      expect(result!.candidates[0].name).toBe("Tent A");
+      expect(result!.candidates[0].categoryName).toBe("Uncategorized");
+      expect(result!.candidates[0].categoryEmoji).toBeDefined();
+    });
+
+    it("returns null for non-existent thread", () => {
+      const result = getThreadWithCandidates(db, 9999);
+      expect(result).toBeNull();
+    });
+  });
+
+  describe("createCandidate", () => {
+    it("adds candidate to thread with all item-compatible fields", () => {
+      const thread = createThread(db, { name: "Tent Options" });
+      const candidate = createCandidate(db, thread.id, {
+        name: "Tent A",
+        weightGrams: 1200,
+        priceCents: 30000,
+        categoryId: 1,
+        notes: "Ultralight 2-person",
+        productUrl: "https://example.com/tent",
+      });
+
+      expect(candidate).toBeDefined();
+      expect(candidate.id).toBeGreaterThan(0);
+      expect(candidate.threadId).toBe(thread.id);
+      expect(candidate.name).toBe("Tent A");
+      expect(candidate.weightGrams).toBe(1200);
+      expect(candidate.priceCents).toBe(30000);
+      expect(candidate.categoryId).toBe(1);
+      expect(candidate.notes).toBe("Ultralight 2-person");
+      expect(candidate.productUrl).toBe("https://example.com/tent");
+    });
+  });
+
+  describe("updateCandidate", () => {
+    it("updates candidate fields, returns updated candidate", () => {
+      const thread = createThread(db, { name: "Test" });
+      const candidate = createCandidate(db, thread.id, {
+        name: "Original",
+        categoryId: 1,
+      });
+
+      const updated = updateCandidate(db, candidate.id, {
+        name: "Updated Name",
+        priceCents: 15000,
+      });
+
+      expect(updated).toBeDefined();
+      expect(updated!.name).toBe("Updated Name");
+      expect(updated!.priceCents).toBe(15000);
+    });
+
+    it("returns null for non-existent candidate", () => {
+      const result = updateCandidate(db, 9999, { name: "Ghost" });
+      expect(result).toBeNull();
+    });
+  });
+
+  describe("deleteCandidate", () => {
+    it("removes candidate, returns deleted candidate", () => {
+      const thread = createThread(db, { name: "Test" });
+      const candidate = createCandidate(db, thread.id, {
+        name: "To Delete",
+        categoryId: 1,
+      });
+
+      const deleted = deleteCandidate(db, candidate.id);
+      expect(deleted).toBeDefined();
+      expect(deleted!.name).toBe("To Delete");
+
+      // Verify it's gone
+      const result = getThreadWithCandidates(db, thread.id);
+      expect(result!.candidates).toHaveLength(0);
+    });
+
+    it("returns null for non-existent candidate", () => {
+      const result = deleteCandidate(db, 9999);
+      expect(result).toBeNull();
+    });
+  });
+
+  describe("updateThread", () => {
+    it("updates thread name", () => {
+      const thread = createThread(db, { name: "Original" });
+      const updated = updateThread(db, thread.id, { name: "Renamed" });
+
+      expect(updated).toBeDefined();
+      expect(updated!.name).toBe("Renamed");
+    });
+
+    it("returns null for non-existent thread", () => {
+      const result = updateThread(db, 9999, { name: "Ghost" });
+      expect(result).toBeNull();
+    });
+  });
+
+  describe("deleteThread", () => {
+    it("removes thread and cascading candidates", () => {
+      const thread = createThread(db, { name: "To Delete" });
+      createCandidate(db, thread.id, { name: "Candidate", categoryId: 1 });
+
+      const deleted = deleteThread(db, thread.id);
+      expect(deleted).toBeDefined();
+      expect(deleted!.name).toBe("To Delete");
+
+      // Thread and candidates gone
+      const result = getThreadWithCandidates(db, thread.id);
+      expect(result).toBeNull();
+    });
+
+    it("returns null for non-existent thread", () => {
+      const result = deleteThread(db, 9999);
+      expect(result).toBeNull();
+    });
+  });
+
+  describe("resolveThread", () => {
+    it("atomically creates collection item from candidate data and archives thread", () => {
+      const thread = createThread(db, { name: "Tent Decision" });
+      const candidate = createCandidate(db, thread.id, {
+        name: "Winner Tent",
+        weightGrams: 1200,
+        priceCents: 30000,
+        categoryId: 1,
+        notes: "Best choice",
+        productUrl: "https://example.com/tent",
+      });
+
+      const result = resolveThread(db, thread.id, candidate.id);
+      expect(result.success).toBe(true);
+      expect(result.item).toBeDefined();
+      expect(result.item!.name).toBe("Winner Tent");
+      expect(result.item!.weightGrams).toBe(1200);
+      expect(result.item!.priceCents).toBe(30000);
+      expect(result.item!.categoryId).toBe(1);
+      expect(result.item!.notes).toBe("Best choice");
+      expect(result.item!.productUrl).toBe("https://example.com/tent");
+
+      // Thread should be resolved
+      const resolved = getThreadWithCandidates(db, thread.id);
+      expect(resolved!.status).toBe("resolved");
+      expect(resolved!.resolvedCandidateId).toBe(candidate.id);
+    });
+
+    it("fails if thread is not active", () => {
+      const thread = createThread(db, { name: "Already Resolved" });
+      const candidate = createCandidate(db, thread.id, {
+        name: "Winner",
+        categoryId: 1,
+      });
+      resolveThread(db, thread.id, candidate.id);
+
+      // Try to resolve again
+      const result = resolveThread(db, thread.id, candidate.id);
+      expect(result.success).toBe(false);
+      expect(result.error).toBeDefined();
+    });
+
+    it("fails if candidate is not in thread", () => {
+      const thread1 = createThread(db, { name: "Thread 1" });
+      const thread2 = createThread(db, { name: "Thread 2" });
+      const candidate = createCandidate(db, thread2.id, {
+        name: "Wrong Thread",
+        categoryId: 1,
+      });
+
+      const result = resolveThread(db, thread1.id, candidate.id);
+      expect(result.success).toBe(false);
+      expect(result.error).toBeDefined();
+    });
+
+    it("fails if candidate not found", () => {
+      const thread = createThread(db, { name: "Test" });
+      const result = resolveThread(db, thread.id, 9999);
+      expect(result.success).toBe(false);
+      expect(result.error).toBeDefined();
+    });
+  });
+});