diff --git a/index.ts b/index.ts
index a24fd68..3b89580 100644
--- a/index.ts
+++ b/index.ts
@@ -18,6 +18,7 @@ import { formatReflections } from "./src/reflection";
 import { verdictGlyph, verdictSummary, formatFindings } from "./src/review";
 import type { ReviewResult } from "./src/types";
 import { executeBatch, type SendChatMessage } from "./src/executor";
+import { cleanupStaleWorktrees } from "./src/worktree";
 import {
 	loadConfig,
 	resolveTaskArg,
@@ -256,6 +257,17 @@ async function executePlanBatches(
 			autoReview: config.execution.autoReview,
 			saveReviews: config.execution.saveReviews,
 		});
+
+		// Clean up stale worktrees from interrupted runs before starting.
+		if (config.execution.worktrees !== "never" && projectDir) {
+			const removed = cleanupStaleWorktrees(projectDir, progress.getKey());
+			if (removed.length > 0) {
+				ctx.ui.notify(
+					`Cleaned up ${removed.length} stale worktree(s) from previous run.`,
+					"info",
+				);
+			}
+		}
 	}
 
 	// Track failed task IDs across batches to block downstream tasks
diff --git a/src/executor.ts b/src/executor.ts
index 53bcf2b..4ee895e 100644
--- a/src/executor.ts
+++ b/src/executor.ts
@@ -26,6 +26,7 @@ import {
 	verdictGlyph,
 	verdictSummary,
 } from "./review";
+import { createWorktree, mergeWorktree, removeWorktree } from "./worktree";
 import {
 	runAgentSession,
 	writeFileSafe,
@@ -388,6 +389,20 @@ export async function runTask(
 /**
  * Execute a batch of tasks (sequentially or in parallel)
  */
+// ─── Worktree Decision ──────────────────────────────────────────────────────
+
+/** Determine if worktree isolation should be used based on config + mode. */
+function shouldUseWorktrees(config: RalpiConfig, isParallel: boolean): boolean {
+	switch (config.execution.worktrees) {
+		case "always":
+			return true;
+		case "parallel":
+			return isParallel;
+		default:
+			return false; // "never"
+	}
+}
+
 export async function executeBatch(
 	tasks: Task[],
 	project: Project,
@@ -443,6 +458,8 @@ export async function executeBatch(
 	const shouldParallel =
 		options?.parallel && tasks.length > 0 && config.execution.maxParallel > 0;
 
+	const useWorktree = shouldUseWorktrees(config, !!shouldParallel);
+
 	if (shouldParallel) {
 		await executeBatchParallel(
 			tasks,
@@ -453,6 +470,7 @@ export async function executeBatch(
 			sendChatMessage,
 			projectDir,
 			roundRobin,
+			useWorktree,
 		);
 		return;
 	}
@@ -468,6 +486,11 @@ export async function executeBatch(
 				ctx,
 				sendChatMessage,
 				projectDir,
+				undefined, // parallelState
+				undefined, // assignedModel
+				undefined, // roundRobin
+				undefined, // batchRender
+				useWorktree,
 			);
 		} catch (error) {
 			// Task failed — stop the batch. Dependent tasks are blocked by
@@ -500,6 +523,7 @@ async function executeBatchParallel(
 	sendChatMessage?: SendChatMessage,
 	projectDir?: string,
 	roundRobin?: ModelRoundRobin | null,
+	useWorktree?: boolean,
 ): Promise<void> {
 	const maxParallel = config.execution.maxParallel;
 	const sharedState: ParallelWidgetState = new Map();
@@ -611,6 +635,7 @@ async function executeBatchParallel(
 				assignedModel,
 				roundRobin,
 				requestBatchRender,
+				useWorktree,
 			)
 				.catch((error) => {
 					// Safety net: one task failure should never crash the batch.
@@ -668,6 +693,7 @@ async function executeTask(
 	assignedModel?: unknown,
 	roundRobin?: ModelRoundRobin | null,
 	batchRender?: () => void,
+	useWorktree?: boolean,
 ): Promise<void> {
 	// Model failover: when a provider/API is down, cycle through available models.
 	// Pi's built-in retry (via SettingsManager) handles transient errors with
@@ -683,6 +709,21 @@ async function executeTask(
 	);
 	let currentModel: unknown = assignedModel ?? implModel ?? config.model;
 
+	// ── Worktree isolation ──
+	// When enabled, the task runs in a separate git worktree so parallel tasks
+	// can't stomp each other's files, and review/commit see a clean single-task
+	// diff. `worktreeDir` is used for agent cwd + git ops; `projectDir` stays as
+	// the main repo dir for state saves (reflections, reviews, progress.json).
+	const wt = useWorktree
+		? createWorktree(
+				projectDir,
+				config.paths.stateDir,
+				task.id,
+				progress.getKey(),
+			)
+		: null;
+	const worktreeDir = wt?.dir ?? projectDir;
+
 	while (modelAttempt < maxModelAttempts) {
 		// On subsequent model attempts, advance to the next model.
 		// Uses advance() instead of assign() so we don't get stuck on
@@ -714,7 +755,7 @@ async function executeTask(
 				depReflections,
 				ctx,
 				sendChatMessage,
-				projectDir,
+				worktreeDir,
 				parallelState,
 				currentModel,
 				batchRender,
@@ -736,9 +777,9 @@ async function executeTask(
 					let attempt = 0;
 
 					try {
-						while (hasUncommittedChanges(projectDir)) {
-							const status = getGitStatusPorcelain(projectDir);
-							const reviewDiff = getGitDiff(projectDir);
+						while (hasUncommittedChanges(worktreeDir)) {
+							const status = getGitStatusPorcelain(worktreeDir);
+							const reviewDiff = getGitDiff(worktreeDir);
 							if (!reviewDiff && !status) break;
 
 							const reviewPrompt = buildReviewPromptUncommitted(
@@ -761,7 +802,7 @@ async function executeTask(
 									ctx,
 									config,
 									reviewPrompt,
-									projectDir,
+									worktreeDir,
 									`review for ${task.id} · ${task.title}${
 										attempt > 0 ? ` (attempt ${attempt + 1})` : ""
 									}`,
@@ -871,7 +912,7 @@ async function executeTask(
 								depReflections,
 								ctx,
 								sendChatMessage,
-								projectDir,
+								worktreeDir,
 								parallelState,
 								currentModel,
 								batchRender,
@@ -897,12 +938,12 @@ async function executeTask(
 						}
 
 						// ── Commit (after review passes or retries exhausted) ──
-						if (hasUncommittedChanges(projectDir)) {
+						if (hasUncommittedChanges(worktreeDir)) {
 							const commitResult = await runCommitSession(
 								ctx,
 								config,
 								task,
-								projectDir,
+								worktreeDir,
 								currentModel,
 								roundRobin,
 								sendChatMessage,
@@ -927,12 +968,12 @@ async function executeTask(
 				} else if (config.execution.autoCommit) {
 					// ── Commit only (no review) — legacy path ──
 					try {
-						if (hasUncommittedChanges(projectDir)) {
+						if (hasUncommittedChanges(worktreeDir)) {
 							const commitResult = await runCommitSession(
 								ctx,
 								config,
 								task,
-								projectDir,
+								worktreeDir,
 								currentModel,
 								roundRobin,
 								sendChatMessage,
@@ -957,7 +998,7 @@ async function executeTask(
 				} else if (config.execution.autoReview) {
 					// ── Review only (no commit) — reviews latest commit — legacy path ──
 					try {
-						const commitInfo = getLatestCommitDiff(projectDir);
+						const commitInfo = getLatestCommitDiff(worktreeDir);
 						if (commitInfo && commitInfo.diff) {
 							const reviewPrompt = buildReviewPrompt(
 								task,
@@ -980,7 +1021,7 @@ async function executeTask(
 									ctx,
 									config,
 									reviewPrompt,
-									projectDir,
+									worktreeDir,
 									`review for ${task.id} · ${task.title}`,
 									`review-${task.id}`,
 									config.execution.reviewTimeoutMs,
@@ -1057,6 +1098,30 @@ async function executeTask(
 					);
 				}
 
+				// ── Merge worktree back to main ──
+				// After the commit lands on the worktree branch, merge it into the
+				// main repo so downstream tasks see the changes. On conflict, the task
+				// is marked failed and the worktree is retained for inspection.
+				if (wt) {
+					const mergeResult = mergeWorktree(projectDir, wt.branch, task.id);
+					if (!mergeResult.success) {
+						sendChatMessage?.(
+							`✗ ${task.id} · ${task.title} — merge conflict, worktree retained at ${wt.dir}\n  ${mergeResult.message}`,
+						);
+						progress.markFailed(task.id, mergeResult.message);
+						try {
+							updateTaskInFile(project.sourcePath, task.id, "failed");
+						} catch {
+							// Best-effort
+						}
+						roundRobin?.release(task.id);
+						return;
+					}
+					// Merge succeeded — clean up the worktree.
+					removeWorktree(projectDir, wt);
+					sendChatMessage?.(`✓ merged worktree for ${task.id} into main`);
+				}
+
 				// Mark completed with all metadata
 				progress.markCompleted(
 					task.id,
@@ -1103,6 +1168,7 @@ async function executeTask(
 				}`,
 				"error",
 			);
+			if (wt) removeWorktree(projectDir, wt);
 			roundRobin?.release(task.id);
 			return;
 		} catch (error) {
@@ -1118,6 +1184,7 @@ async function executeTask(
 			}
 			sendChatMessage?.(`✗ ${task.id} · ${task.title} — ${errorMsg}`);
 			ctx.ui.notify(`Task ${task.id} failed: ${errorMsg}`, "error");
+			if (wt) removeWorktree(projectDir, wt);
 			return;
 		}
 	}
@@ -1133,6 +1200,7 @@ async function executeTask(
 		`Task ${task.id} failed: all configured models exhausted`,
 		"error",
 	);
+	if (wt) removeWorktree(projectDir, wt);
 }
 
 // ─── Save Reflection to File ────────────────────────────────────────────────
diff --git a/src/types.ts b/src/types.ts
index a3356e2..66147a0 100644
--- a/src/types.ts
+++ b/src/types.ts
@@ -238,6 +238,12 @@ export interface RalpiConfig {
 		reviewBlockOnFail: boolean;
 		/** Maximum total duration for the entire loop execution in milliseconds (0 = no limit). Checked between batches — in-progress tasks finish naturally. */
 		loopTimeoutMs: number;
+		/** Isolate each task in a separate git worktree so parallel tasks can't
+		 *  stomp each other's files, and review/commit see a clean single-task diff.
+		 *  - "never":   all tasks run in the shared working tree (default, backward compat)
+		 *  - "parallel": only when maxParallel > 1 and mode is parallel
+		 *  - "always":  every task gets its own worktree */
+		worktrees: "always" | "parallel" | "never";
 	};
 	prompts: {
 		/** Additional context injected into every task prompt */
@@ -272,6 +278,7 @@ export const DEFAULT_CONFIG: RalpiConfig = {
 		maxReviewRetries: 2, // 2 re-execution attempts on review rejection before giving up
 		reviewBlockOnFail: false, // false = commit anyway after retries exhausted
 		loopTimeoutMs: 0, // 0 = no limit
+		worktrees: "never", // worktree isolation per task
 	},
 	prompts: {
 		projectContext: "",
diff --git a/src/worktree.ts b/src/worktree.ts
new file mode 100644
index 0000000..591c537
--- /dev/null
+++ b/src/worktree.ts
@@ -0,0 +1,268 @@
+import * as path from "node:path";
+import { ensureDir } from "./utils";
+
+// ─── Types ───────────────────────────────────────────────────────────────────
+
+export interface WorktreeHandle {
+	/** Absolute path to the worktree working directory. */
+	dir: string;
+	/** Branch name: `ralpi/<prdKey>/<taskId>`. */
+	branch: string;
+	/** Main repo directory (where the primary working tree lives). */
+	mainDir: string;
+}
+
+export interface MergeResult {
+	success: boolean;
+	/** File paths that conflicted (empty when merge succeeds). */
+	conflicts: string[];
+	/** Human-readable status message. */
+	message: string;
+}
+
+// ─── Git Helpers ─────────────────────────────────────────────────────────────
+
+/** Run a git command, returning trimmed stdout. Returns null on failure. */
+function git(args: string, cwd: string): string | null {
+	const { execSync } = require("node:child_process") as {
+		execSync: (cmd: string, opts: object) => string;
+	};
+	try {
+		return execSync(`git ${args}`, {
+			cwd,
+			encoding: "utf-8",
+			stdio: ["pipe", "pipe", "pipe"],
+		}).trim();
+	} catch {
+		return null;
+	}
+}
+
+/** Run a git command that may fail; returns { ok, stdout, stderr }. */
+function gitRaw(
+	args: string,
+	cwd: string,
+): { ok: boolean; stdout: string; stderr: string } {
+	const { execSync } = require("node:child_process") as {
+		execSync: (cmd: string, opts: object) => string;
+	};
+	try {
+		const stdout = execSync(`git ${args}`, {
+			cwd,
+			encoding: "utf-8",
+			stdio: ["pipe", "pipe", "pipe"],
+		});
+		return { ok: true, stdout: stdout.trim(), stderr: "" };
+	} catch (err: unknown) {
+		const e = err as {
+			stdout?: string;
+			stderr?: string;
+			message?: string;
+		};
+		return {
+			ok: false,
+			stdout: (e.stdout ?? "").toString().trim(),
+			stderr: (e.stderr ?? "").toString().trim(),
+		};
+	}
+}
+
+/** Check if a directory is inside a git repository. */
+export function isGitRepo(dir: string): boolean {
+	return git("rev-parse --git-dir", dir) !== null;
+}
+
+/** Get the current HEAD commit hash of a directory. */
+export function getGitHead(dir: string): string | null {
+	return git("rev-parse HEAD", dir);
+}
+
+/** Get the current branch name of a directory. */
+export function getCurrentBranch(dir: string): string | null {
+	return git("rev-parse --abbrev-ref HEAD", dir);
+}
+
+// ─── Worktree Lifecycle ──────────────────────────────────────────────────────
+
+/**
+ * Path to the worktree directory for a given task.
+ * Lives inside `.ralpi/worktrees/<taskId>` in the main repo so all ralpi
+ * state stays co-located. The directory itself is untracked git metadata
+ * (registered in `.git/worktrees/`), so it won't pollute `git status`
+ * in the main working tree.
+ */
+export function worktreePath(
+	mainDir: string,
+	stateDir: string,
+	taskId: string,
+): string {
+	return path.join(mainDir, stateDir, "worktrees", taskId);
+}
+
+/**
+ * Normalise a task ID into a valid git branch suffix.
+ * Zero-padded IDs like "01" are already valid; this ensures any stray
+ * characters are replaced.
+ */
+function safeBranchSuffix(taskId: string): string {
+	return taskId.replace(/[^a-zA-Z0-9_-]/g, "-");
+}
+
+/**
+ * Create a git worktree for a task.
+ *
+ * The worktree is created at `<mainDir>/.ralpi/worktrees/<taskId>` on a new
+ * branch `ralpi/<prdKey>/<taskId>`, based at `baseRef` (defaults to the
+ * current HEAD of `mainDir`).
+ *
+ * Returns null if `mainDir` is not a git repo or the worktree creation fails.
+ */
+export function createWorktree(
+	mainDir: string,
+	stateDir: string,
+	taskId: string,
+	prdKey: string,
+	baseRef?: string,
+): WorktreeHandle | null {
+	if (!isGitRepo(mainDir)) return null;
+
+	const ref = baseRef ?? getGitHead(mainDir);
+	if (!ref) return null;
+
+	const safeId = safeBranchSuffix(taskId);
+	const branch = `ralpi/${prdKey}/${safeId}`;
+	const wtDir = worktreePath(mainDir, stateDir, taskId);
+
+	// Ensure the parent directory exists so `git worktree add` can create
+	// the worktree directory inside it.
+	ensureDir(path.dirname(wtDir));
+
+	// Remove a stale worktree directory if one exists (e.g. from a crashed
+	// previous run). `git worktree add` fails if the path already exists.
+	// We prune first to clean up any metadata for removed-but-not-pruned dirs.
+	git("worktree prune", mainDir);
+	const existing = git(`worktree list --porcelain`, mainDir);
+	if (existing && existing.includes(`worktree ${wtDir}`)) {
+		// A worktree at this path is already registered — remove it.
+		git(`worktree remove --force "${wtDir}"`, mainDir);
+	}
+	// Also delete a stale branch if it exists from a previous run.
+	git(`branch -D "${branch}"`, mainDir);
+
+	const result = gitRaw(
+		`worktree add -b "${branch}" "${wtDir}" "${ref}"`,
+		mainDir,
+	);
+	if (!result.ok) {
+		// Fall back to detached HEAD worktree if branch creation fails
+		// (e.g. the branch name somehow conflicts).
+		const fallback = gitRaw(
+			`worktree add --detach "${wtDir}" "${ref}"`,
+			mainDir,
+		);
+		if (!fallback.ok) return null;
+	}
+
+	return { dir: wtDir, branch, mainDir };
+}
+
+/**
+ * Merge a worktree's branch back into the current branch of the main repo.
+ *
+ * Uses `--no-ff` to always create a merge commit, preserving the task
+ * branch's history. On conflict, the merge is aborted and the conflicts
+ * are returned so the caller can mark the task as failed.
+ */
+export function mergeWorktree(
+	mainDir: string,
+	branch: string,
+	taskId: string,
+): MergeResult {
+	// Attempt the merge.
+	const result = gitRaw(`merge --no-ff --no-edit "${branch}"`, mainDir);
+
+	if (result.ok) {
+		return {
+			success: true,
+			conflicts: [],
+			message: `Merged ${branch} into ${getCurrentBranch(mainDir) ?? "HEAD"}`,
+		};
+	}
+
+	// Merge failed — likely conflicts. Collect the list of conflicting files.
+	const status = git("diff --name-only --diff-filter=U", mainDir) ?? "";
+	const conflicts = status
+		.split("\n")
+		.map((l) => l.trim())
+		.filter(Boolean);
+
+	// Abort the merge so the main repo's working tree is left clean.
+	git("merge --abort", mainDir);
+
+	return {
+		success: false,
+		conflicts,
+		message:
+			conflicts.length > 0
+				? `Merge conflicts in: ${conflicts.join(", ")}`
+				: `Merge of ${branch} failed: ${result.stderr || result.stdout}`,
+	};
+}
+
+/**
+ * Remove a worktree and delete its branch.
+ *
+ * Called after a successful merge to clean up. Safe to call even if the
+ * worktree or branch no longer exists.
+ */
+export function removeWorktree(mainDir: string, wt: WorktreeHandle): void {
+	git(`worktree remove --force "${wt.dir}"`, mainDir);
+	git(`branch -D "${wt.branch}"`, mainDir);
+	git("worktree prune", mainDir);
+}
+
+/**
+ * Clean up stale worktrees from interrupted runs.
+ *
+ * Lists all worktrees whose branches start with `ralpi/<prdKey>/` and
+ * removes them. Called at the start of a loop to ensure a clean slate.
+ * Returns the list of removed worktree directories.
+ */
+export function cleanupStaleWorktrees(
+	mainDir: string,
+	prdKey: string,
+): string[] {
+	const removed: string[] = [];
+
+	// Prune metadata for worktree directories that no longer exist on disk.
+	git("worktree prune", mainDir);
+
+	const list = git("worktree list --porcelain", mainDir);
+	if (!list) return removed;
+
+	// Parse worktree list: each entry is `worktree <path>` followed by metadata.
+	const wtLines = list
+		.split("\n")
+		.filter((l) => l.startsWith("worktree "))
+		.map((l) => l.slice("worktree ".length).trim());
+
+	for (const wtDir of wtLines) {
+		// Skip the main working tree (always first in the list).
+		if (path.resolve(wtDir) === path.resolve(mainDir)) continue;
+
+		// Check if this worktree is on a ralpi branch for this PRD.
+		const branch = git(`rev-parse --abbrev-ref HEAD`, wtDir);
+		if (!branch) continue;
+		if (!branch.startsWith(`ralpi/${prdKey}/`)) continue;
+
+		// Remove the worktree and its branch.
+		git(`worktree remove --force "${wtDir}"`, mainDir);
+		if (branch !== "HEAD" && branch !== "detached") {
+			git(`branch -D "${branch}"`, mainDir);
+		}
+		removed.push(wtDir);
+	}
+
+	git("worktree prune", mainDir);
+	return removed;
+}