diff --git a/src/Sync/SyncResult.php b/src/Sync/SyncResult.php
new file mode 100644
index 0000000..01d9790
--- /dev/null
+++ b/src/Sync/SyncResult.php
@@ -0,0 +1,116 @@
+<?php
+/**
+ * Immutable sync operation result.
+ *
+ * @package WPContentSync
+ */
+
+namespace WPContentSync\Sync;
+
+final class SyncResult {
+	private bool $successful;
+	private int $created;
+	private int $updated;
+	private int $skipped;
+	private int $conflicts;
+
+	/** @var array<int, string> */
+	private array $errors;
+
+	/**
+	 * @param array<int, string> $errors Error messages.
+	 */
+	private function __construct( bool $successful, int $created, int $updated, int $skipped, int $conflicts, array $errors ) {
+		$this->successful = $successful;
+		$this->created    = max( 0, $created );
+		$this->updated    = max( 0, $updated );
+		$this->skipped    = max( 0, $skipped );
+		$this->conflicts  = max( 0, $conflicts );
+		$this->errors     = array_values( array_map( 'strval', $errors ) );
+	}
+
+	/**
+	 * @param array<string, int> $counts Result counts.
+	 */
+	public static function success( array $counts = array() ): self {
+		return new self(
+			true,
+			(int) ( $counts['created'] ?? 0 ),
+			(int) ( $counts['updated'] ?? 0 ),
+			(int) ( $counts['skipped'] ?? 0 ),
+			(int) ( $counts['conflicts'] ?? 0 ),
+			array()
+		);
+	}
+
+	/**
+	 * @param array<int, string> $errors Error messages.
+	 */
+	public static function failure( array $errors ): self {
+		return new self( false, 0, 0, 0, 0, $errors );
+	}
+
+	/**
+	 * @param array<int, self> $results Results to merge.
+	 */
+	public static function merge( array $results ): self {
+		$successful = true;
+		$created    = 0;
+		$updated    = 0;
+		$skipped    = 0;
+		$conflicts  = 0;
+		$errors     = array();
+
+		foreach ( $results as $result ) {
+			$successful = $successful && $result->isSuccessful();
+			$created   += $result->created();
+			$updated   += $result->updated();
+			$skipped   += $result->skipped();
+			$conflicts += $result->conflicts();
+			$errors     = array_merge( $errors, $result->errors() );
+		}
+
+		return new self( $successful, $created, $updated, $skipped, $conflicts, $errors );
+	}
+
+	public function isSuccessful(): bool {
+		return $this->successful;
+	}
+
+	public function created(): int {
+		return $this->created;
+	}
+
+	public function updated(): int {
+		return $this->updated;
+	}
+
+	public function skipped(): int {
+		return $this->skipped;
+	}
+
+	public function conflicts(): int {
+		return $this->conflicts;
+	}
+
+	/**
+	 * @return array<int, string>
+	 */
+	public function errors(): array {
+		return $this->errors;
+	}
+
+	/**
+	 * @return array<string, mixed>
+	 */
+	public function toArray(): array {
+		return array(
+			'successful' => $this->successful,
+			'created'    => $this->created,
+			'updated'    => $this->updated,
+			'skipped'    => $this->skipped,
+			'conflicts'  => $this->conflicts,
+			'errors'     => $this->errors,
+		);
+	}
+}
diff --git a/tests/Unit/Sync/SyncResultTest.php b/tests/Unit/Sync/SyncResultTest.php
new file mode 100644
index 0000000..48c3511
--- /dev/null
+++ b/tests/Unit/Sync/SyncResultTest.php
@@ -0,0 +1,72 @@
+<?php
+/**
+ * Tests for sync result summaries.
+ *
+ * @package WPContentSync
+ */
+
+namespace WPContentSync\Tests\Unit\Sync;
+
+use PHPUnit\Framework\TestCase;
+use WPContentSync\Sync\SyncResult;
+
+class SyncResultTest extends TestCase {
+	public function test_it_tracks_successful_counts(): void {
+		$result = SyncResult::success(
+			array(
+				'created'   => 2,
+				'updated'   => 3,
+				'skipped'   => 1,
+				'conflicts' => 1,
+			)
+		);
+
+		self::assertTrue( $result->isSuccessful() );
+		self::assertSame( 2, $result->created() );
+		self::assertSame( 3, $result->updated() );
+		self::assertSame( 1, $result->skipped() );
+		self::assertSame( 1, $result->conflicts() );
+		self::assertSame( array(), $result->errors() );
+		self::assertSame(
+			array(
+				'successful' => true,
+				'created'    => 2,
+				'updated'    => 3,
+				'skipped'    => 1,
+				'conflicts'  => 1,
+				'errors'     => array(),
+			),
+			$result->toArray()
+		);
+	}
+
+	public function test_it_tracks_failed_results(): void {
+		$result = SyncResult::failure( array( 'posts import failed.' ) );
+
+		self::assertFalse( $result->isSuccessful() );
+		self::assertSame( array( 'posts import failed.' ), $result->errors() );
+	}
+
+	public function test_it_merges_multiple_results(): void {
+		$result = SyncResult::merge(
+			array(
+				SyncResult::success( array( 'created' => 1 ) ),
+				SyncResult::success(
+					array(
+						'updated'   => 2,
+						'skipped'   => 1,
+						'conflicts' => 1,
+					)
+				),
+				SyncResult::failure( array( 'terms import failed.' ) ),
+			)
+		);
+
+		self::assertFalse( $result->isSuccessful() );
+		self::assertSame( 1, $result->created() );
+		self::assertSame( 2, $result->updated() );
+		self::assertSame( 1, $result->skipped() );
+		self::assertSame( 1, $result->conflicts() );
+		self::assertSame( array( 'terms import failed.' ), $result->errors() );
+	}
+}