diff --git a/CHANGELOG.md b/CHANGELOG.md
index d4d71bd..0148ac5 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -25,14 +25,28 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 - **Secret Sharing & Access Control (Phase 3)** (#182)
   - **Secret CRUD API**: Full REST API for password manager functionality
-    - Create secrets with encrypted title, username, password, URL, notes (POST `/v1/secrets`)
-    - List user's secrets with pagination (GET `/v1/secrets`)
-    - View secret details (GET `/v1/secrets/{secret}`)
-    - Update secrets with automatic version incrementing (PATCH `/v1/secrets/{secret}`)
+    (#187)
+    - Create secrets with encrypted title, username, password, URL, notes
+      (POST `/v1/secrets`)
+    - List user's secrets with filter parameter: `all` (default), `owned`, `shared`
+      (via SecretShare) (GET `/v1/secrets?filter={type}`)
+    - Filter validation via `IndexSecretRequest` (rejects invalid filter values)
+    - Query optimization: Role IDs cached to avoid N+1 queries
+    - DRY implementation: Shared filter logic extracted to `Secret::scopeSharedWith()`
+    - Empty role array optimization: Skips `orWhereIn` when user has no roles
+    - View secret details with owner or share-based access (GET
+      `/v1/secrets/{secret}`)
+    - Update secrets with automatic version incrementing (PATCH
+      `/v1/secrets/{secret}`)
     - Soft delete secrets (DELETE `/v1/secrets/{secret}`)
-    - Owner-based authorization via `SecretPolicy`
-    - Validation via `StoreSecretRequest` and `UpdateSecretRequest`
-    - 17 comprehensive Controller tests
+    - Authorization via `SecretPolicy` with 9 methods: viewAny, view, create,
+      update, delete, restore, forceDelete, share, viewShares
+    - Permission hierarchy: admin > write > read (via
+      `Secret::userHasPermission()`)
+    - Share-based access respects expiration dates and permission levels
+    - Validation via `StoreSecretRequest`, `UpdateSecretRequest`, `IndexSecretRequest`
+    - 22 comprehensive Controller tests covering CRUD + share-based access
+      scenarios
   - **Secret Sharing API**: Grant/revoke access to secrets
     - Grant read/write/admin access to users OR roles (POST `/v1/secrets/{secret}/shares`)
     - List all shares for a secret (GET `/v1/secrets/{secret}/shares`)
diff --git a/app/Http/Controllers/Api/V1/SecretController.php b/app/Http/Controllers/Api/V1/SecretController.php
index 4c5cf70..8dc1f6d 100644
--- a/app/Http/Controllers/Api/V1/SecretController.php
+++ b/app/Http/Controllers/Api/V1/SecretController.php
@@ -7,6 +7,7 @@
 namespace App\Http\Controllers\Api\V1;
 
 use App\Http\Controllers\Controller;
+use App\Http\Requests\IndexSecretRequest;
 use App\Http\Requests\StoreSecretRequest;
 use App\Http\Requests\UpdateSecretRequest;
 use App\Models\Secret;
@@ -103,15 +104,29 @@ private function assignFields(Secret $secret, Request $request): bool
     /**
      * Display a listing of secrets accessible to the authenticated user.
      */
-    public function index(Request $request): JsonResponse
+    public function index(IndexSecretRequest $request): JsonResponse
     {
         $this->authorize('viewAny', Secret::class);
 
         /** @var \App\Models\User $user */
         $user = $request->user();
 
-        // Query secrets owned by user
-        $query = Secret::where('owner_id', $user->id);
+        // Cache role IDs to avoid N+1 queries
+        /** @var array<int> $roleIds */
+        $roleIds = $user->roles->pluck('id')->toArray();
+
+        // Build query based on filter parameter
+        $filter = $request->validated('filter', 'all');
+
+        // Use match expression with explicit return value capture
+        $query = match ($filter) {
+            'owned' => Secret::query()->where('owner_id', $user->id),
+            'shared' => Secret::query()->sharedWith($user, $roleIds),
+            default => Secret::query()->where(function ($q) use ($user, $roleIds) {
+                $q->where('owner_id', $user->id)
+                    ->orWhere(fn ($subQuery) => $subQuery->sharedWith($user, $roleIds));
+            }),
+        };
 
         // Pagination
         /** @var int $perPageInput */
diff --git a/app/Http/Requests/IndexSecretRequest.php b/app/Http/Requests/IndexSecretRequest.php
new file mode 100644
index 0000000..60621e2
--- /dev/null
+++ b/app/Http/Requests/IndexSecretRequest.php
@@ -0,0 +1,53 @@
+<?php
+
+/*
+ * SPDX-FileCopyrightText: 2025 SecPal Contributors
+ *
+ * SPDX-License-Identifier: AGPL-3.0-or-later
+ */
+
+declare(strict_types=1);
+
+namespace App\Http\Requests;
+
+use Illuminate\Foundation\Http\FormRequest;
+use Illuminate\Validation\Rule;
+
+class IndexSecretRequest extends FormRequest
+{
+    /**
+     * Determine if the user is authorized to make this request.
+     */
+    public function authorize(): bool
+    {
+        return true;
+    }
+
+    /**
+     * Get the validation rules that apply to the request.
+     *
+     * @return array<string, \Illuminate\Contracts\Validation\ValidationRule|array<mixed>|string>
+     */
+    public function rules(): array
+    {
+        return [
+            'filter' => [
+                'sometimes',
+                'string',
+                Rule::in(['all', 'owned', 'shared']),
+            ],
+        ];
+    }
+
+    /**
+     * Get custom messages for validator errors.
+     *
+     * @return array<string, string>
+     */
+    public function messages(): array
+    {
+        return [
+            'filter.in' => 'The filter must be one of: all, owned, shared.',
+        ];
+    }
+}
diff --git a/app/Models/Secret.php b/app/Models/Secret.php
index 2ba006c..4b30d89 100644
--- a/app/Models/Secret.php
+++ b/app/Models/Secret.php
@@ -56,6 +56,7 @@
  * @method static \Illuminate\Database\Eloquent\Builder|Secret owned(string $userId)
  * @method static \Illuminate\Database\Eloquent\Builder|Secret active()
  * @method static \Illuminate\Database\Eloquent\Builder|Secret expired()
+ * @method static \Illuminate\Database\Eloquent\Builder|Secret sharedWith(User $user, array<int> $roleIds)
  */
 class Secret extends Model
 {
@@ -369,4 +370,31 @@ public function userHasPermission(User $user, string $permission): bool
             default => false,
         };
     }
+
+    /**
+     * Scope query to secrets shared with the given user.
+     *
+     * Filters secrets that have active shares (not expired) where the user
+     * or any of the user's roles have access.
+     *
+     * @param  \Illuminate\Database\Eloquent\Builder<Secret>  $query
+     * @param  array<int>  $roleIds
+     * @return \Illuminate\Database\Eloquent\Builder<Secret>
+     */
+    public function scopeSharedWith(\Illuminate\Database\Eloquent\Builder $query, User $user, array $roleIds): \Illuminate\Database\Eloquent\Builder
+    {
+        return $query->whereHas('shares', function ($q) use ($user, $roleIds) {
+            $q->where(function ($shareQuery) use ($user, $roleIds) {
+                $shareQuery->where('user_id', $user->id);
+                // Only add role check if user has roles (avoids empty array query)
+                if (! empty($roleIds)) {
+                    $shareQuery->orWhereIn('role_id', $roleIds);
+                }
+            })
+                ->where(function ($expiryQuery) {
+                    $expiryQuery->whereNull('expires_at')
+                        ->orWhere('expires_at', '>', now());
+                });
+        });
+    }
 }
diff --git a/app/Policies/SecretPolicy.php b/app/Policies/SecretPolicy.php
index aab7ad4..87c71a8 100644
--- a/app/Policies/SecretPolicy.php
+++ b/app/Policies/SecretPolicy.php
@@ -74,4 +74,24 @@ public function forceDelete(User $user, Secret $secret): bool
     {
         return $secret->owner_id === $user->id;
     }
+
+    /**
+     * Determine whether the user can share the secret with others.
+     *
+     * Only the owner or users with admin permission can grant shares.
+     */
+    public function share(User $user, Secret $secret): bool
+    {
+        return $secret->userHasPermission($user, 'admin');
+    }
+
+    /**
+     * Determine whether the user can view the shares of the secret.
+     *
+     * Only the owner or users with admin permission can see who has access.
+     */
+    public function viewShares(User $user, Secret $secret): bool
+    {
+        return $secret->userHasPermission($user, 'admin');
+    }
 }
diff --git a/tests/Feature/Controllers/Api/V1/SecretControllerTest.php b/tests/Feature/Controllers/Api/V1/SecretControllerTest.php
index cf773f1..468a73d 100644
--- a/tests/Feature/Controllers/Api/V1/SecretControllerTest.php
+++ b/tests/Feature/Controllers/Api/V1/SecretControllerTest.php
@@ -560,3 +560,114 @@
         $response->assertForbidden();
     });
 });
+
+describe('SecretController - Filter Parameter', function () {
+    test('filter=owned returns only owned secrets', function () {
+        // Arrange: Create owned secret
+        $ownSecret = createTestSecret([
+            'tenant_id' => $this->tenant->id,
+            'owner_id' => $this->user->id,
+            'title_plain' => 'My Secret',
+        ]);
+
+        // Create secret shared with user
+        $owner = User::factory()->create();
+        $sharedSecret = createTestSecret([
+            'tenant_id' => $this->tenant->id,
+            'owner_id' => $owner->id,
+            'title_plain' => 'Shared Secret',
+        ]);
+        \App\Models\SecretShare::create([
+            'secret_id' => $sharedSecret->id,
+            'user_id' => $this->user->id,
+            'permission' => 'read',
+            'granted_by' => $owner->id,
+            'granted_at' => now(),
+        ]);
+
+        // Act
+        $response = getJson('/v1/secrets?filter=owned');
+
+        // Assert
+        $response->assertOk()
+            ->assertJsonCount(1, 'data')
+            ->assertJsonPath('data.0.title', 'My Secret');
+    });
+
+    test('filter=shared returns only shared secrets', function () {
+        // Arrange: Create owned secret
+        createTestSecret([
+            'tenant_id' => $this->tenant->id,
+            'owner_id' => $this->user->id,
+            'title_plain' => 'My Secret',
+        ]);
+
+        // Create secret shared with user
+        $owner = User::factory()->create();
+        $sharedSecret = createTestSecret([
+            'tenant_id' => $this->tenant->id,
+            'owner_id' => $owner->id,
+            'title_plain' => 'Shared Secret',
+        ]);
+        \App\Models\SecretShare::create([
+            'secret_id' => $sharedSecret->id,
+            'user_id' => $this->user->id,
+            'permission' => 'read',
+            'granted_by' => $owner->id,
+            'granted_at' => now(),
+        ]);
+
+        // Act
+        $response = getJson('/v1/secrets?filter=shared');
+
+        // Assert
+        $response->assertOk()
+            ->assertJsonCount(1, 'data')
+            ->assertJsonPath('data.0.title', 'Shared Secret');
+    });
+
+    test('filter=all returns both owned and shared secrets', function () {
+        // Arrange: Create owned secret
+        createTestSecret([
+            'tenant_id' => $this->tenant->id,
+            'owner_id' => $this->user->id,
+            'title_plain' => 'My Secret',
+        ]);
+
+        // Create secret shared with user
+        $owner = User::factory()->create();
+        $sharedSecret = createTestSecret([
+            'tenant_id' => $this->tenant->id,
+            'owner_id' => $owner->id,
+            'title_plain' => 'Shared Secret',
+        ]);
+        \App\Models\SecretShare::create([
+            'secret_id' => $sharedSecret->id,
+            'user_id' => $this->user->id,
+            'permission' => 'read',
+            'granted_by' => $owner->id,
+            'granted_at' => now(),
+        ]);
+
+        // Act
+        $response = getJson('/v1/secrets?filter=all');
+
+        // Assert
+        $response->assertOk()
+            ->assertJsonCount(2, 'data');
+    });
+
+    test('filter parameter rejects invalid values', function () {
+        // Act
+        $response = getJson('/v1/secrets?filter=invalid');
+
+        // Assert
+        $response->assertStatus(422)
+            ->assertJsonValidationErrors(['filter'])
+            ->assertJsonFragment([
+                'filter' => [
+                    'The filter must be one of: all, owned, shared.',
+                ],
+            ]);
+    });
+});
diff --git a/tests/Feature/Policies/SecretPolicyTest.php b/tests/Feature/Policies/SecretPolicyTest.php
new file mode 100644
index 0000000..89ecd1f
--- /dev/null
+++ b/tests/Feature/Policies/SecretPolicyTest.php
@@ -0,0 +1,121 @@
+<?php
+
+// SPDX-FileCopyrightText: 2025 SecPal Contributors
+//
+// SPDX-License-Identifier: AGPL-3.0-or-later
+
+use App\Models\Secret;
+use App\Models\SecretShare;
+use App\Models\TenantKey;
+use App\Models\User;
+use App\Policies\SecretPolicy;
+use Illuminate\Foundation\Testing\RefreshDatabase;
+
+uses(RefreshDatabase::class);
+
+beforeEach(function (): void {
+    TenantKey::setKekPath(getTestKekPath());
+    TenantKey::generateKek();
+
+    $keys = TenantKey::generateEnvelopeKeys();
+    $this->tenant = TenantKey::create($keys);
+
+    $this->owner = User::factory()->create();
+    $this->otherUser = User::factory()->create();
+    $this->policy = new SecretPolicy;
+
+    $this->secret = new Secret;
+    $this->secret->tenant_id = $this->tenant->id;
+    $this->secret->owner_id = $this->owner->id;
+    $this->secret->title_plain = 'Test Secret';
+    $this->secret->save();
+});
+
+afterEach(function (): void {
+    cleanupTestKekFile();
+    TenantKey::setKekPath(null);
+});
+
+describe('SecretPolicy - Basic Permissions', function () {
+    test('owner can restore secret', function (): void {
+        expect($this->policy->restore($this->owner, $this->secret))->toBeTrue();
+    });
+
+    test('non-owner cannot restore secret', function (): void {
+        expect($this->policy->restore($this->otherUser, $this->secret))->toBeFalse();
+    });
+
+    test('owner can force delete secret', function (): void {
+        expect($this->policy->forceDelete($this->owner, $this->secret))->toBeTrue();
+    });
+
+    test('non-owner cannot force delete secret', function (): void {
+        expect($this->policy->forceDelete($this->otherUser, $this->secret))->toBeFalse();
+    });
+});
+
+describe('SecretPolicy - Share Permissions', function () {
+    test('owner can share secret', function (): void {
+        expect($this->policy->share($this->owner, $this->secret))->toBeTrue();
+    });
+
+    test('non-owner cannot share secret', function (): void {
+        expect($this->policy->share($this->otherUser, $this->secret))->toBeFalse();
+    });
+
+    test('user with admin share can share secret', function (): void {
+        SecretShare::create([
+            'secret_id' => $this->secret->id,
+            'user_id' => $this->otherUser->id,
+            'permission' => 'admin',
+            'granted_by' => $this->owner->id,
+            'granted_at' => now(),
+        ]);
+
+        expect($this->policy->share($this->otherUser, $this->secret))->toBeTrue();
+    });
+
+    test('user with write share cannot share secret', function (): void {
+        SecretShare::create([
+            'secret_id' => $this->secret->id,
+            'user_id' => $this->otherUser->id,
+            'permission' => 'write',
+            'granted_by' => $this->owner->id,
+            'granted_at' => now(),
+        ]);
+
+        expect($this->policy->share($this->otherUser, $this->secret))->toBeFalse();
+    });
+
+    test('owner can view shares', function (): void {
+        expect($this->policy->viewShares($this->owner, $this->secret))->toBeTrue();
+    });
+
+    test('non-owner cannot view shares', function (): void {
+        expect($this->policy->viewShares($this->otherUser, $this->secret))->toBeFalse();
+    });
+
+    test('user with admin share can view shares', function (): void {
+        SecretShare::create([
+            'secret_id' => $this->secret->id,
+            'user_id' => $this->otherUser->id,
+            'permission' => 'admin',
+            'granted_by' => $this->owner->id,
+            'granted_at' => now(),
+        ]);
+
+        expect($this->policy->viewShares($this->otherUser, $this->secret))->toBeTrue();
+    });
+
+    test('user with read share cannot view shares', function (): void {
+        SecretShare::create([
+            'secret_id' => $this->secret->id,
+            'user_id' => $this->otherUser->id,
+            'permission' => 'read',
+            'granted_by' => $this->owner->id,
+            'granted_at' => now(),
+        ]);
+
+        expect($this->policy->viewShares($this->otherUser, $this->secret))->toBeFalse();
+    });
+});