diff --git a/packages/host/host.ts b/packages/host/host.ts
index 41609cab..5b3daf19 100755
--- a/packages/host/host.ts
+++ b/packages/host/host.ts
@@ -203,7 +203,14 @@ async function startHost() {
 	}
 
 	let hostConnector = new HostConnector(hostConfig, tlsCa, pluginInfos);
-	let host = new Host(hostConnector, args.config, hostConfig, tlsCa, pluginInfos);
+	let host = new Host(
+		hostConnector,
+		args.config,
+		hostConfig,
+		tlsCa,
+		pluginInfos,
+		...await Host.bootstrap(hostConfig)
+	);
 
 	// Handle interrupts
 	let secondSigint = false;
diff --git a/packages/host/src/Host.ts b/packages/host/src/Host.ts
index c170e1ad..c9395724 100644
--- a/packages/host/src/Host.ts
+++ b/packages/host/src/Host.ts
@@ -263,12 +263,21 @@ export default class Host extends lib.Link {
 	_disconnecting = false;
 	_shuttingDown = false;
 
+	static async bootstrap(hostConfig: lib.HostConfig) {
+		const modsDirectory = hostConfig.get("host.mods_directory");
+		await fs.ensureDir(modsDirectory);
+		return [
+			await lib.ModStore.fromDirectory(modsDirectory),
+		] as const;
+	}
+
 	constructor(
 		connector: HostConnector,
 		hostConfigPath: string,
 		hostConfig: lib.HostConfig,
 		tlsCa: string | undefined,
-		pluginInfos: lib.PluginNodeEnvInfo[]
+		pluginInfos: lib.PluginNodeEnvInfo[],
+		public modStore: lib.ModStore,
 	) {
 		super(connector);
 		this.tlsCa = tlsCa;
@@ -478,6 +487,77 @@ export default class Host extends lib.Link {
 		}
 	}
 
+	async downloadMod(mod: lib.ModRecord) {
+		let streamId = await this.send(new lib.ModDownloadRequest(mod.name, mod.version, mod.sha1));
+
+		let url = new URL(this.config.get("host.controller_url"));
+		url.pathname += `api/stream/${streamId}`;
+		let response = await phin({
+			url, method: "GET",
+			core: { ca: this.tlsCa } as object,
+			stream: true,
+		});
+
+		const file = lib.ModInfo.filename(mod.name, mod.version);
+		const filePath = path.join(this.modStore.modsDirectory, file);
+		const tempFilePath = filePath.replace(/(\.zip)?$/, ".tmp.zip");
+		const writeStream = fs.createWriteStream(tempFilePath, { flags: "w" });
+		await events.once(writeStream, "open");
+		response.pipe(writeStream);
+		await finished(writeStream);
+		await fs.rename(tempFilePath, filePath);
+
+		const modInfo = await this.modStore.loadFile(file);
+		if (mod.sha1 && mod.sha1 !== modInfo.sha1) {
+			throw new Error(`Checksum mismatch downloading ${file} from controller`);
+		}
+		logger.info(`Downloaded ${file} from controller`);
+		return modInfo;
+	}
+
+	private _fetchModQueue = new lib.AsyncSerialCallback(this._fetchModInternal.bind(this));
+
+	async fetchMod(mod: lib.ModRecord) {
+		return await this._fetchModQueue.invoke(mod);
+	}
+
+	private async _fetchModInternal(mod: lib.ModRecord) {
+		// The mod may have already been downloaded in a previous call
+		let modInfo = this.modStore.getMod(mod.name, mod.version);
+		if (modInfo && (!mod.sha1 || mod.sha1 === modInfo.sha1)) {
+			return modInfo;
+		}
+
+		// The mods folder may be shared with the controller and thus
+		// already have this mod, try loading it.
+		try {
+			modInfo = await this.modStore.loadMod(mod.name, mod.version);
+		} catch (err: any) {
+			if (err.code !== "ENOENT") {
+				throw err;
+			}
+		}
+		if (modInfo && (!mod.sha1 || mod.sha1 === modInfo.sha1)) {
+			return modInfo;
+		}
+
+		// Fetch the mod from the controller.
+		return await this.downloadMod(mod);
+	}
+
+	async fetchMods(mods: Iterable<lib.ModRecord>) {
+		const modInfos: Promise<lib.ModInfo>[] = [];
+		for (const mod of mods) {
+			// XXX These mods ship with Factorio, but the list of mods may
+			// change and should not be hardcoded here.
+			if (["core", "base"].includes(mod.name)) {
+				continue;
+			}
+			modInfos.push(this.fetchMod(mod));
+		}
+		return await Promise.all(modInfos);
+	}
+
 	async handleInstanceAssignInternalRequest(request: lib.InstanceAssignInternalRequest) {
 		let { instanceId, config } = request;
 		let instanceInfo = this.instanceInfos.get(instanceId);
diff --git a/packages/host/src/Instance.ts b/packages/host/src/Instance.ts
index f68bdd24..aab54cd1 100644
--- a/packages/host/src/Instance.ts
+++ b/packages/host/src/Instance.ts
@@ -646,9 +646,7 @@ rcon.print(game.table_to_json(players))`.replace(/\r?\n/g, " ");
 
 		// TODO validate factorioVersion
 
-		if (!this._host.config.get("host.mods_directory_is_shared")) {
-			throw new Error("Fetching mods is not implemented");
-		}
+		const mods = await this._host.fetchMods(modPack.mods.values());
 
 		await fs.ensureDir(this.path("mods"));
 
@@ -668,8 +666,8 @@ rcon.print(game.table_to_json(players))`.replace(/\r?\n/g, " ");
 
 		// Add mods from mod the pack
 		const modsDir = this._host.config.get("host.mods_directory");
-		for (let mod of this.activeModPack.mods.values()) {
-			const modFile = `${mod.name}_${mod.version}.zip`;
+		for (let mod of mods) {
+			const modFile = mod.filename;
 			const target = path.join(modsDir, modFile);
 			const link = this.path("mods", modFile);
 
diff --git a/packages/lib/src/config/definitions.ts b/packages/lib/src/config/definitions.ts
index 282e5b60..098e8522 100644
--- a/packages/lib/src/config/definitions.ts
+++ b/packages/lib/src/config/definitions.ts
@@ -21,6 +21,7 @@ ControllerGroup.define({
 	name: "mods_directory",
 	title: "Mods Directory",
 	description: "Path to directory where mods shared with the cluster are stored.",
+	restartRequired: true,
 	type: "string",
 	initial_value: "mods",
 });
@@ -202,16 +203,10 @@ HostGroup.define({
 	name: "mods_directory",
 	title: "Mods Directory",
 	description: "Path to directory where mods for instances are cached.",
+	restartRequired: true,
 	type: "string",
 	initial_value: "mods",
 });
-HostGroup.define({
-	name: "mods_directory_is_shared",
-	title: "Mods Directory is Shared",
-	description: "True if the mods directory is shared with the controller.",
-	type: "boolean",
-	initial_value: true,
-});
 HostGroup.define({
 	name: "instances_directory",
 	description: "Path to directory to store instances in.",
@@ -264,7 +259,6 @@ export class HostConfig extends classes.Config {
 	get(name: "host.id"): number;
 	get(name: "host.factorio_directory"): string;
 	get(name: "host.mods_directory"): string;
-	get(name: "host.mods_directory_is_shared"): boolean;
 	get(name: "host.instances_directory"): string;
 	get(name: "host.controller_url"): string;
 	get(name: "host.controller_token"): string;
diff --git a/test/integration/clusterio.js b/test/integration/clusterio.js
index b076b439..b9931847 100644
--- a/test/integration/clusterio.js
+++ b/test/integration/clusterio.js
@@ -32,9 +32,12 @@ async function startAltHost() {
 	let configPath = path.join("temp", "test", config);
 	await fs.remove(configPath);
 	await fs.remove(path.join("temp", "test", "alt-instances"));
+	await fs.remove(path.join("temp", "test", "alt-mods"));
 	await execCtl(`host create-config --id 5 --name alt-host --generate-token --output ${config}`);
 	await exec(`node ../../packages/host --config ${config} config set host.tls_ca ../../test/file/tls/cert.pem`);
 	await exec(`node ../../packages/host --config ${config} config set host.instances_directory alt-instances`);
+	await exec(`node ../../packages/host --config ${config} config set host.factorio_directory ../../factorio`);
+	await exec(`node ../../packages/host --config ${config} config set host.mods_directory alt-mods`);
 	return await spawn("alt-host:", `node ../../packages/host run --config ${config}`, /Started host/);
 }
 
@@ -176,6 +179,23 @@ describe("Integration of Clusterio", function() {
 				assert(hosts.has(5), "Host list was not updated");
 			});
 		});
+		it("should download mods from controller", async function() {
+			// On windows there's currently no way to automate graceful shutdown of the host
+			// process as CTRL+C is some weird terminal thing and SIGINT isn't a thing.
+			if (process.platform === "win32") {
+				this.skip();
+			}
+
+			slowTest(this);
+			await runWithAltHost(async () => {
+				const clusterioLib = path.join("temp", "test", "alt-mods", "clusterio_lib_0.1.2.zip");
+				assert(!await fs.pathExists(clusterioLib), "mod was downloaded before the test");
+				await execCtl("instance create alt-mod --id 98");
+				await execCtl("instance assign alt-mod 5");
+				await execCtl("instance save create alt-mod");
+				assert(await fs.pathExists(clusterioLib), "mod was not downloaded by the test");
+			});
+		});
 	});
 
 	describe("clusterioctl", function() {