diff --git a/src/host/config.ts b/src/host/config.ts
index af58b1f..a8e33d5 100644
--- a/src/host/config.ts
+++ b/src/host/config.ts
@@ -2,6 +2,7 @@ import type { UNode, UElement, URoot, ComponentFn, UComponent } from "../core/sc
 import { isURoot, isUPrimitive } from "../core/schema.js";
 import { Context } from "../core/context.js";
 import type { Fiber } from "./fiber.js";
+import { reconcileProps, commitEffects } from "./reconcile.js";
 
 export interface HostConfig<TTag extends string, Instance, RootCtx> {
   name: string;
@@ -122,6 +123,19 @@ export function createRoot<TTag extends string, Instance, RootCtx>(
     context: rootContext,
     rootFiber: null,
     render(node: UNode) {
+      if (this.rootFiber) {
+        const payloadChildren = isURoot(node) ? (node as URoot).children : [node];
+        for (let i = 0; i < payloadChildren.length; i++) {
+          const childFiber = this.rootFiber.children[i];
+          if (childFiber) {
+            reconcileProps(childFiber, payloadChildren[i]!, host as HostConfig<string, Instance, unknown>, ctx as unknown);
+          }
+        }
+        commitEffects(this.rootFiber, host as HostConfig<string, Instance, unknown>, ctx as unknown);
+        host.emit?.("root.render", `root_${Date.now()}`, { childCount: payloadChildren.length });
+        return;
+      }
+
       const root: Fiber<Instance> = {
         instance: undefined as unknown as Instance,
         tag: "#root",
diff --git a/src/host/reconcile.ts b/src/host/reconcile.ts
new file mode 100644
index 0000000..a740448
--- /dev/null
+++ b/src/host/reconcile.ts
@@ -0,0 +1,157 @@
+import { effect } from "@preact/signals-core";
+import type { Fiber, Effect } from "./fiber.js";
+import type { HostConfig } from "./config.js";
+import type { UNode, UElement } from "../core/schema.js";
+import { isUPrimitive, isURoot } from "../core/schema.js";
+
+interface PendingUpdate {
+  fiber: Fiber<unknown>;
+  nextNode: UNode;
+}
+
+let pendingUpdates: PendingUpdate[] = [];
+let flushScheduled = false;
+
+export function scheduleUpdate<I>(
+  fiber: Fiber<I>,
+  nextNode: UNode,
+  host: HostConfig<string, I, unknown>,
+  ctx: unknown,
+): void {
+  pendingUpdates.push({ fiber: fiber as Fiber<unknown>, nextNode });
+  if (!flushScheduled) {
+    flushScheduled = true;
+    queueMicrotask(() => flushUpdates(host as HostConfig<string, unknown, unknown>, ctx));
+  }
+}
+
+export function flushUpdates(
+  host: HostConfig<string, unknown, unknown>,
+  ctx: unknown,
+): void {
+  flushScheduled = false;
+  const updates = pendingUpdates.splice(0);
+
+  for (const { fiber, nextNode } of updates) {
+    reconcileProps(fiber, nextNode, host, ctx);
+  }
+
+  const seen = new Set<Fiber<unknown>>();
+  for (const { fiber } of updates) {
+    let root: Fiber<unknown> | null = fiber;
+    while (root.parent) root = root.parent;
+    if (!seen.has(root)) {
+      seen.add(root);
+      commitEffects(root, host, ctx);
+    }
+  }
+}
+
+export function reconcileProps<I>(
+  fiber: Fiber<I>,
+  nextNode: UNode,
+  host: HostConfig<string, I, unknown>,
+  ctx: unknown,
+): void {
+  if (isUPrimitive(nextNode)) {
+    if (fiber.tag === "#text") {
+      const text = nextNode === null ? "" : String(nextNode);
+      if (fiber.props.text !== text) {
+        const nextProps = { text };
+        const payload = host.prepareUpdate?.(
+          fiber.instance,
+          fiber.tag as never,
+          fiber.props,
+          nextProps,
+          ctx as never,
+        );
+        if (payload !== null && payload !== undefined) {
+          fiber.effect = { type: "update", payload };
+          fiber.prevProps = { ...fiber.props };
+          fiber.props = nextProps;
+        }
+      }
+    }
+    return;
+  }
+
+  if (isURoot(nextNode)) {
+    const rootChildren = nextNode.children;
+    const count = Math.min(fiber.children.length, rootChildren.length);
+    for (let i = 0; i < count; i++) {
+      reconcileProps(fiber.children[i]!, rootChildren[i]!, host, ctx);
+    }
+    return;
+  }
+
+  const el = nextNode as UElement;
+
+  if (typeof el.type === "function") {
+    const component = el.type as (props: Record<string, unknown>) => UNode;
+    const out = component({ ...el.props, children: el.children });
+    reconcileProps(fiber, out, host, ctx);
+    return;
+  }
+
+  if (fiber.tag !== "#text" && fiber.tag !== el.type) return;
+
+  const nextProps = el.props as Record<string, unknown>;
+  const payload = host.prepareUpdate?.(
+    fiber.instance,
+    fiber.tag as never,
+    fiber.props,
+    nextProps,
+    ctx as never,
+  );
+
+  if (payload !== null && payload !== undefined) {
+    fiber.effect = { type: "update", payload };
+    fiber.prevProps = { ...fiber.props };
+    fiber.props = nextProps;
+  }
+
+  const count = Math.min(fiber.children.length, el.children.length);
+  for (let i = 0; i < count; i++) {
+    reconcileProps(fiber.children[i]!, el.children[i]!, host, ctx);
+  }
+}
+
+export function commitEffects<I>(
+  fiber: Fiber<I>,
+  host: HostConfig<string, I, unknown>,
+  ctx: unknown,
+): void {
+  if (fiber.effect?.type === "update") {
+    const updateEffect = fiber.effect as Effect<I> & { type: "update"; payload: unknown };
+    host.commitUpdate?.(
+      fiber.instance,
+      updateEffect.payload,
+      fiber.tag as never,
+      fiber.prevProps ?? {},
+      fiber.props,
+      ctx as never,
+    );
+  }
+  for (const child of fiber.children) {
+    commitEffects(child, host, ctx);
+  }
+  fiber.effect = null;
+}
+
+export function wireSignalToFiber<I>(
+  fiber: Fiber<I>,
+  signalGetter: () => UNode,
+  host: HostConfig<string, I, unknown>,
+  ctx: unknown,
+): void {
+  const disposer = effect(() => {
+    const nextNode = signalGetter();
+    scheduleUpdate(fiber, nextNode, host, ctx);
+  });
+  fiber.signalDisposers.push(disposer);
+}
+
+export function resetUpdateQueue(): void {
+  pendingUpdates = [];
+  flushScheduled = false;
+}
\ No newline at end of file
diff --git a/src/mod.ts b/src/mod.ts
index 2af5285..748ba33 100644
--- a/src/mod.ts
+++ b/src/mod.ts
@@ -21,5 +21,7 @@ export type { HostConfig, Root } from "./host/config.js";
 
 export type { Fiber, Effect } from "./host/fiber.js";
 
+export { scheduleUpdate, flushUpdates, reconcileProps, commitEffects, wireSignalToFiber, resetUpdateQueue } from "./host/reconcile.js";
+
 export { TransformRegistry, childCtx, matchesSchema, ctx as transformCtx } from "./transform/registry.js";
 export type { TransformContext, TransformFn, TransformRule } from "./transform/registry.js";
\ No newline at end of file
diff --git a/test/signal-driven-updates.test.ts b/test/signal-driven-updates.test.ts
new file mode 100644
index 0000000..d2d60f9
--- /dev/null
+++ b/test/signal-driven-updates.test.ts
@@ -0,0 +1,299 @@
+import { describe, it, expect, vi, beforeEach, afterEach } from "vitest";
+import { h } from "../src/core/h.js";
+import { signal, batch } from "../src/core/reactive.js";
+import { createRoot as createHostRoot } from "../src/host/config.js";
+import type { HostConfig } from "../src/host/config.js";
+import type { Fiber } from "../src/host/fiber.js";
+import { scheduleUpdate, flushUpdates, reconcileProps, commitEffects, wireSignalToFiber, resetUpdateQueue } from "../src/host/reconcile.js";
+
+function makeTrackingHost() {
+  const prepareUpdateCalls: { instance: string; tag: string; prevProps: Record<string, unknown>; nextProps: Record<string, unknown> }[] = [];
+  const commitUpdateCalls: { instance: string; payload: unknown; tag: string; prevProps: Record<string, unknown>; nextProps: Record<string, unknown> }[] = [];
+  const instances: { tag: string; props: Record<string, unknown> }[] = [];
+  const texts: string[] = [];
+  const appends: { parent: string; child: string }[] = [];
+
+  const host: HostConfig<string, string, Record<string, unknown>> = {
+    name: "tracking",
+    createRootContext: () => ({}),
+    createInstance: (tag, props) => {
+      const id = `${tag}_${instances.length}`;
+      instances.push({ tag, props });
+      return id;
+    },
+    createTextInstance: (text) => {
+      texts.push(text);
+      return `text_${texts.length - 1}`;
+    },
+    appendChild: (parent, child) => {
+      appends.push({ parent, child });
+    },
+    prepareUpdate: (instance, tag, prevProps, nextProps) => {
+      prepareUpdateCalls.push({ instance, tag, prevProps: { ...prevProps }, nextProps: { ...nextProps } });
+      const changed: Record<string, unknown> = {};
+      let hasChanges = false;
+      for (const key of Object.keys(nextProps)) {
+        if (prevProps[key] !== nextProps[key]) {
+          changed[key] = nextProps[key];
+          hasChanges = true;
+        }
+      }
+      for (const key of Object.keys(prevProps)) {
+        if (!(key in nextProps)) {
+          changed[key] = undefined;
+          hasChanges = true;
+        }
+      }
+      return hasChanges ? changed : null;
+    },
+    commitUpdate: (instance, payload, tag, prevProps, nextProps) => {
+      commitUpdateCalls.push({ instance, payload, tag, prevProps: { ...prevProps }, nextProps: { ...nextProps } });
+    },
+  };
+
+  return { host, prepareUpdateCalls, commitUpdateCalls, instances, texts, appends };
+}
+
+describe("signal-driven-updates", () => {
+  beforeEach(() => {
+    resetUpdateQueue();
+  });
+
+  describe("wireSignalToFiber", () => {
+    it("signal change triggers prepareUpdate + commitUpdate", async () => {
+      const { host, prepareUpdateCalls, commitUpdateCalls } = makeTrackingHost();
+      const color = signal("red");
+
+      const root = createHostRoot(host, {});
+      root.render(h("div", { color: color.value }));
+
+      const divFiber = root.rootFiber!.children[0]!;
+      expect(divFiber.tag).toBe("div");
+
+      wireSignalToFiber(
+        divFiber,
+        () => h("div", { color: color.value }),
+        host as HostConfig<string, string, unknown>,
+        {},
+      );
+
+      expect(prepareUpdateCalls.length).toBe(0);
+      expect(commitUpdateCalls.length).toBe(0);
+
+      color.value = "blue";
+
+      await new Promise<void>((resolve) => {
+        queueMicrotask(() => resolve());
+      });
+
+      expect(prepareUpdateCalls.length).toBeGreaterThanOrEqual(1);
+      const lastPrepare = prepareUpdateCalls[prepareUpdateCalls.length - 1]!;
+      expect(lastPrepare.tag).toBe("div");
+      expect(lastPrepare.prevProps.color).toBe("red");
+      expect(lastPrepare.nextProps.color).toBe("blue");
+
+      expect(commitUpdateCalls.length).toBeGreaterThanOrEqual(1);
+      const lastCommit = commitUpdateCalls[commitUpdateCalls.length - 1]!;
+      expect(lastCommit.instance).toBe(divFiber.instance);
+      expect(lastCommit.payload).toEqual({ color: "blue" });
+    });
+
+    it("signal effect disposer stored in fiber.signalDisposers", () => {
+      const { host } = makeTrackingHost();
+      const color = signal("red");
+
+      const root = createHostRoot(host, {});
+      root.render(h("div", { color: color.value }));
+
+      const divFiber = root.rootFiber!.children[0]!;
+      const beforeCount = divFiber.signalDisposers.length;
+
+      wireSignalToFiber(
+        divFiber,
+        () => h("div", { color: color.value }),
+        host as HostConfig<string, string, unknown>,
+        {},
+      );
+
+      expect(divFiber.signalDisposers.length).toBe(beforeCount + 1);
+      expect(typeof divFiber.signalDisposers[divFiber.signalDisposers.length - 1]).toBe("function");
+    });
+
+    it("disposing signal via signalDisposers stops updates", async () => {
+      const { host, prepareUpdateCalls } = makeTrackingHost();
+      const color = signal("red");
+
+      const root = createHostRoot(host, {});
+      root.render(h("div", { color: color.value }));
+
+      const divFiber = root.rootFiber!.children[0]!;
+      wireSignalToFiber(
+        divFiber,
+        () => h("div", { color: color.value }),
+        host as HostConfig<string, string, unknown>,
+        {},
+      );
+
+      await new Promise<void>((resolve) => {
+        queueMicrotask(() => resolve());
+      });
+      resetUpdateQueue();
+
+      const disposer = divFiber.signalDisposers.pop()!;
+      disposer();
+
+      const callCountBefore = prepareUpdateCalls.filter((c) => c.tag === "div").length;
+      color.value = "green";
+
+      await new Promise<void>((resolve) => {
+        queueMicrotask(() => resolve());
+      });
+
+      expect(prepareUpdateCalls.filter((c) => c.tag === "div").length).toBe(callCountBefore);
+    });
+  });
+
+  describe("batch of signal changes", () => {
+    it("batch of signal changes results in single reconciliation pass", async () => {
+      const { host, prepareUpdateCalls, commitUpdateCalls } = makeTrackingHost();
+      const color = signal("red");
+      const size = signal("small");
+
+      const root = createHostRoot(host, {});
+      root.render(h("div", { color: color.value, size: size.value }));
+
+      const divFiber = root.rootFiber!.children[0]!;
+
+      wireSignalToFiber(
+        divFiber,
+        () => h("div", { color: color.value, size: size.value }),
+        host as HostConfig<string, string, unknown>,
+        {},
+      );
+
+      await new Promise<void>((resolve) => {
+        queueMicrotask(() => resolve());
+      });
+      resetUpdateQueue();
+      prepareUpdateCalls.length = 0;
+      commitUpdateCalls.length = 0;
+
+      batch(() => {
+        color.value = "blue";
+        size.value = "large";
+      });
+
+      await new Promise<void>((resolve) => {
+        queueMicrotask(() => resolve());
+      });
+
+      expect(prepareUpdateCalls.filter((c) => c.tag === "div").length).toBe(1);
+      expect(commitUpdateCalls.filter((c) => c.tag === "div").length).toBe(1);
+    });
+  });
+
+  describe("render() re-renderable", () => {
+    it("second render reconciles props against existing fiber tree", () => {
+      const { host, prepareUpdateCalls, commitUpdateCalls, instances } = makeTrackingHost();
+      const root = createHostRoot(host, {});
+      root.render(h("div", { color: "red" }, "hello"));
+
+      expect(instances.length).toBe(1);
+      const instanceCountBefore = instances.length;
+
+      root.render(h("div", { color: "blue" }, "hello"));
+
+      expect(instances.length).toBe(instanceCountBefore);
+
+      const divPrepareCalls = prepareUpdateCalls.filter((c) => c.tag === "div");
+      expect(divPrepareCalls.length).toBe(1);
+      expect(divPrepareCalls[0]!.prevProps.color).toBe("red");
+      expect(divPrepareCalls[0]!.nextProps.color).toBe("blue");
+
+      const divCommitCalls = commitUpdateCalls.filter((c) => c.tag === "div");
+      expect(divCommitCalls.length).toBe(1);
+      expect(divCommitCalls[0]!.payload).toEqual({ color: "blue" });
+    });
+
+    it("second render does not create duplicate instances", () => {
+      const { host, instances } = makeTrackingHost();
+      const root = createHostRoot(host, {});
+      root.render(h("div", { color: "red" }));
+
+      expect(instances.length).toBe(1);
+      root.render(h("div", { color: "blue" }));
+      expect(instances.length).toBe(1);
+    });
+
+    it("prepareUpdate is called for changed props on re-render", () => {
+      const { host, prepareUpdateCalls } = makeTrackingHost();
+      const root = createHostRoot(host, {});
+      root.render(h("span", { label: "a" }));
+      root.render(h("span", { label: "b" }));
+
+      const spanPrepares = prepareUpdateCalls.filter((c) => c.tag === "span");
+      expect(spanPrepares.length).toBe(1);
+      expect(spanPrepares[0]!.prevProps.label).toBe("a");
+      expect(spanPrepares[0]!.nextProps.label).toBe("b");
+    });
+  });
+
+  describe("prepareUpdate/commitUpdate optional", () => {
+    it("host without prepareUpdate is a no-op on re-render", () => {
+      const host: HostConfig<string, string, Record<string, unknown>> = {
+        name: "minimal",
+        createRootContext: () => ({}),
+        createInstance: (tag) => tag,
+        createTextInstance: (text) => text,
+        appendChild: () => {},
+      };
+      const root = createHostRoot(host, {});
+      root.render(h("div", { color: "red" }));
+      expect(() => root.render(h("div", { color: "blue" }))).not.toThrow();
+    });
+  });
+
+  describe("commitEffects top-down order", () => {
+    it("parent commitUpdate fires before child commitUpdate", () => {
+      const { host, commitUpdateCalls } = makeTrackingHost();
+      const root = createHostRoot(host, {});
+      root.render(h("div", { color: "red" }, h("span", { label: "a" })));
+
+      root.render(h("div", { color: "blue" }, h("span", { label: "b" })));
+
+      const tags = commitUpdateCalls.map((c) => c.tag);
+      const divIdx = tags.indexOf("div");
+      const spanIdx = tags.indexOf("span");
+      expect(divIdx).toBeLessThan(spanIdx);
+    });
+  });
+
+  describe("reconcileProps direct call", () => {
+    it("updates fiber props and sets effect when prepareUpdate returns payload", () => {
+      const { host } = makeTrackingHost();
+      const root = createHostRoot(host, {});
+      root.render(h("div", { color: "red" }));
+
+      const divFiber = root.rootFiber!.children[0]!;
+      expect(divFiber.props.color).toBe("red");
+
+      reconcileProps(divFiber, h("div", { color: "blue" }), host as HostConfig<string, string, unknown>, {});
+
+      expect(divFiber.props.color).toBe("blue");
+      expect(divFiber.effect).not.toBeNull();
+      expect(divFiber.effect!.type).toBe("update");
+      expect(divFiber.prevProps!.color).toBe("red");
+    });
+
+    it("no effect when props are unchanged", () => {
+      const { host } = makeTrackingHost();
+      const root = createHostRoot(host, {});
+      root.render(h("div", { color: "red" }));
+
+      const divFiber = root.rootFiber!.children[0]!;
+      reconcileProps(divFiber, h("div", { color: "red" }), host as HostConfig<string, string, unknown>, {});
+
+      expect(divFiber.effect).toBeNull();
+    });
+  });
+});
\ No newline at end of file