diff --git a/src/Attribute/Attribute.php b/src/Attribute/Attribute.php
index b0b9911..047c62f 100644
--- a/src/Attribute/Attribute.php
+++ b/src/Attribute/Attribute.php
@@ -65,7 +65,7 @@ public function getValidations()
      */
     public function generateSchema()
     {
-        return [
+        $schema = [
             'name' => $this->name,
             'type' => $this->getType(),
             'mutability' => $this->mutability,
@@ -75,6 +75,12 @@ public function generateSchema()
             'multiValued' => $this->getMultiValued(),
             'caseExact' => false
         ];
+
+        if ($this->description !== null) {
+            $schema['description'] = $this->description;
+        }
+
+        return $schema;
     }
 
     public function setMultiValued($multiValued)
@@ -164,6 +170,13 @@ public function setParent($parent)
         return $this;
     }
 
+    public function setDescription(?string $description)
+    {
+        $this->description = $description;
+
+        return $this;
+    }
+
     protected function isRequested($attributes)
     {
         return empty($attributes) || in_array($this->name, $attributes) || in_array($this->getFullKey(), $attributes) || ($this->parent != null && $this->parent->isRequested($attributes));
diff --git a/src/Attribute/Collection.php b/src/Attribute/Collection.php
index b7c4fb5..beeb78f 100644
--- a/src/Attribute/Collection.php
+++ b/src/Attribute/Collection.php
@@ -9,6 +9,8 @@
 
 class Collection extends AbstractComplex
 {
+    protected $type = 'complex';
+
     protected $attribute;
     protected $multiValued = true;
 
diff --git a/src/Attribute/Constant.php b/src/Attribute/Constant.php
index 6ab312c..5fa0778 100644
--- a/src/Attribute/Constant.php
+++ b/src/Attribute/Constant.php
@@ -3,6 +3,7 @@
 namespace ArieTimmerman\Laravel\SCIMServer\Attribute;
 
 use ArieTimmerman\Laravel\SCIMServer\Exceptions\SCIMException;
+use Illuminate\Database\Eloquent\Builder;
 use Illuminate\Database\Eloquent\Model;
 use ArieTimmerman\Laravel\SCIMServer\Parser\Path;
 
@@ -42,4 +43,44 @@ public function patch($operation, $value, Model &$object, ?Path $path = null)
     {
         throw new SCIMException('Patch operation not supported for constant attributes');
     }
+
+    public function applyComparison(Builder &$query, Path $path, $parentAttribute = null)
+    {
+        $operator = $path->node->operator ?? null;
+        $value = $path->node->compareValue ?? null;
+
+        if ($operator === null) {
+            throw new SCIMException('Invalid comparison on constant attribute');
+        }
+
+        $constantValue = $this->value;
+
+        $matches = $this->valuesAreEqual($constantValue, $value);
+
+        switch ($operator) {
+            case 'pr':
+                $query->whereRaw('1 = 1');
+                return;
+
+            case 'eq':
+                $query->whereRaw($matches ? '1 = 1' : '1 = 0');
+                return;
+
+            case 'ne':
+                $query->whereRaw($matches ? '1 = 0' : '1 = 1');
+                return;
+
+            default:
+                throw new SCIMException(sprintf('Operator "%s" not supported for constant attributes', $operator));
+        }
+    }
+
+    private function valuesAreEqual($constantValue, $compareValue): bool
+    {
+        if (is_string($constantValue) && is_string($compareValue)) {
+            return strcasecmp($constantValue, $compareValue) === 0;
+        }
+
+        return $constantValue === $compareValue;
+    }
 }
diff --git a/src/Filter/Ast/Disjunction.php b/src/Filter/Ast/Disjunction.php
index 3a3cf05..1cdf666 100644
--- a/src/Filter/Ast/Disjunction.php
+++ b/src/Filter/Ast/Disjunction.php
@@ -2,7 +2,7 @@
 
 namespace ArieTimmerman\Laravel\SCIMServer\Filter\Ast;
 
-class Disjunction extends Filter
+class Disjunction extends Term
 {
     /** @var Term[] */
     private array $terms = [];
diff --git a/src/Http/Controllers/ResourceController.php b/src/Http/Controllers/ResourceController.php
index 20ce83f..7cb2830 100644
--- a/src/Http/Controllers/ResourceController.php
+++ b/src/Http/Controllers/ResourceController.php
@@ -7,6 +7,7 @@
 use ArieTimmerman\Laravel\SCIMServer\Helper;
 use ArieTimmerman\Laravel\SCIMServer\Exceptions\SCIMException;
 use ArieTimmerman\Laravel\SCIMServer\ResourceType;
+use ArieTimmerman\Laravel\SCIMServer\SCIMConfig;
 use Illuminate\Database\Eloquent\Model;
 use ArieTimmerman\Laravel\SCIMServer\Events\Delete;
 use ArieTimmerman\Laravel\SCIMServer\Events\Get;
@@ -304,6 +305,24 @@ function (Builder $query) use ($filter, $resourceType) {
         );
     }
 
+    public function crossResourceSearch(Request $request, PolicyDecisionPoint $pdp, SCIMConfig $config)
+    {
+        $input = $request->json()->all();
+
+        if (!is_array($input) || !isset($input['schemas']) || !in_array('urn:ietf:params:scim:api:messages:2.0:SearchRequest', $input['schemas'])) {
+            throw (new SCIMException('Invalid schema. MUST be "urn:ietf:params:scim:api:messages:2.0:SearchRequest"'))->setCode(400);
+        }
+
+        $request->replace($input);
+
+        return $this->runCrossResourceQuery($request, $config);
+    }
+
+    public function crossResourceIndex(Request $request, PolicyDecisionPoint $pdp, SCIMConfig $config)
+    {
+        return $this->runCrossResourceQuery($request, $config);
+    }
+
     public function search(Request $request, PolicyDecisionPoint $pdp, ResourceType $resourceType){
 
         $input = $request->json()->all();
@@ -319,6 +338,126 @@ public function search(Request $request, PolicyDecisionPoint $pdp, ResourceType
         return $this->index($request, $pdp, $resourceType);
     }
 
+    protected function runCrossResourceQuery(Request $request, SCIMConfig $config): ListResponse
+    {
+        if ($request->has('cursor')) {
+            throw (new SCIMException('Cursor pagination is not supported for cross-resource search'))->setCode(400)->setScimType('invalidCursor');
+        }
+
+        [$attributes, $excludedAttributes] = $this->resolveAttributeParameters($request);
+
+        $count = min(max(0, intVal($request->input('count', config('scim.pagination.defaultPageSize')))), config('scim.pagination.maxPageSize'));
+        $startIndex = max(1, intVal($request->input('startIndex', 1)));
+
+        $resourceTypes = $this->resolveResourceTypesForSearch($config);
+
+        if (empty($resourceTypes)) {
+            return new ListResponse(collect(), $startIndex, 0, $attributes, $excludedAttributes);
+        }
+
+        if ($request->filled('sortBy') && count($resourceTypes) > 1) {
+            throw (new SCIMException('sortBy is only supported when a single resourceType is requested'))->setCode(400)->setScimType('invalidValue');
+        }
+
+        $sortAttribute = null;
+        $sortDirection = $request->input('sortOrder') === 'descending' ? 'desc' : 'asc';
+
+        if ($request->filled('sortBy')) {
+            $sortAttribute = $resourceTypes[0]->getMapping()->getSortAttributeByPath(ParserParser::parse($request->input('sortBy')));
+        }
+
+        $filter = $request->input('filter');
+
+        $resources = collect();
+        $offset = $startIndex - 1;
+        $remaining = $count;
+        $perTypeTotals = [];
+        $totalResults = 0;
+
+        $applyFilter = function (Builder $query, ResourceType $resourceType) use ($filter) {
+            if ($filter === null) {
+                return;
+            }
+
+            try {
+                Helper::scimFilterToLaravelQuery($resourceType, $query, ParserParser::parseFilter($filter));
+            } catch (ParserFilterException $e) {
+                throw (new SCIMException($e->getMessage()))->setCode(400)->setScimType('invalidFilter');
+            }
+        };
+
+        foreach ($resourceTypes as $resourceType) {
+            $countQuery = $resourceType->getQuery();
+            $applyFilter($countQuery, $resourceType);
+
+            $typeTotal = $countQuery->count();
+            $perTypeTotals[] = [$resourceType, $typeTotal];
+            $totalResults += $typeTotal;
+        }
+
+        foreach ($perTypeTotals as [$resourceType, $typeTotal]) {
+            if ($offset >= $typeTotal) {
+                $offset -= $typeTotal;
+                continue;
+            }
+
+            if ($remaining === 0) {
+                break;
+            }
+
+            $dataQuery = $resourceType->getQuery();
+            $applyFilter($dataQuery, $resourceType);
+
+            $dataQuery = $dataQuery->with($resourceType->getWithRelations());
+
+            if ($sortAttribute !== null) {
+                $dataQuery = $dataQuery->orderBy($sortAttribute, $sortDirection);
+            }
+
+            if ($offset > 0) {
+                $dataQuery = $dataQuery->skip($offset);
+            }
+
+            if ($remaining > 0) {
+                $dataQuery = $dataQuery->take($remaining);
+            }
+
+            $items = $dataQuery->get();
+
+            $offset = 0;
+            $remaining -= $items->count();
+
+            foreach ($items as $item) {
+                $resources->push(
+                    Helper::objectToSCIMArray($item, $resourceType, $attributes, $excludedAttributes)
+                );
+            }
+
+            if ($remaining <= 0) {
+                break;
+            }
+        }
+
+        return new ListResponse($resources, $startIndex, $totalResults, $attributes, $excludedAttributes);
+    }
+
+    protected function resolveResourceTypesForSearch(SCIMConfig $config): array
+    {
+        $configurations = $config->getConfig();
+
+        if (empty($configurations)) {
+            return [];
+        }
+
+        $resourceTypes = [];
+
+        foreach ($configurations as $name => $configuration) {
+            $resourceTypes[] = new ResourceType($name, $configuration);
+        }
+
+        return $resourceTypes;
+    }
+
     protected function respondWithResource(Request $request, ResourceType $resourceType, Model $resourceObject, int $status = 200)
     {
         [$attributes, $excludedAttributes] = $this->resolveAttributeParameters($request);
diff --git a/src/RouteProvider.php b/src/RouteProvider.php
index 16408ca..26f8442 100644
--- a/src/RouteProvider.php
+++ b/src/RouteProvider.php
@@ -71,8 +71,9 @@ public static function publicRoutes(array $options = [])
 
     private static function allRoutes(array $options = [])
     {
-        // TODO: Implement POST /.search for cross-resource queries per RFC 7644 §3.4.3.
-        Route::post('.search', [\ArieTimmerman\Laravel\SCIMServer\Http\Controllers\ResourceController::class, 'notImplemented']);
+        Route::get('/', [\ArieTimmerman\Laravel\SCIMServer\Http\Controllers\ResourceController::class, 'crossResourceIndex']);
+        Route::get('', [\ArieTimmerman\Laravel\SCIMServer\Http\Controllers\ResourceController::class, 'crossResourceIndex']);
+        Route::post('.search', [\ArieTimmerman\Laravel\SCIMServer\Http\Controllers\ResourceController::class, 'crossResourceSearch']);
 
         Route::post("/Bulk", [\ArieTimmerman\Laravel\SCIMServer\Http\Controllers\BulkController::class, 'processBulkRequest']);
 
diff --git a/src/SCIMConfig.php b/src/SCIMConfig.php
index e8931db..8a3d63c 100644
--- a/src/SCIMConfig.php
+++ b/src/SCIMConfig.php
@@ -184,7 +184,9 @@ public function remove($value, &$object, $path = null)
                             $fail('The name has already been taken.');
                         }
                     }),
-                    (new MutableCollection('members'))->withSubAttributes(
+                    (new MutableCollection('members'))
+                    ->setDescription('A list of members of the Group.')
+                    ->withSubAttributes(
                         eloquent('value', 'id')->ensure('required'),
                         (new class ('$ref') extends Eloquent {
                             protected function doRead(&$object, $attributes = [])
diff --git a/tests/CrossResourceSearchTest.php b/tests/CrossResourceSearchTest.php
new file mode 100644
index 0000000..250ea7d
--- /dev/null
+++ b/tests/CrossResourceSearchTest.php
@@ -0,0 +1,138 @@
+<?php
+
+namespace ArieTimmerman\Laravel\SCIMServer\Tests;
+
+class CrossResourceSearchTest extends TestCase
+{
+    public function testIndexCombinesResourceTypes()
+    {
+        $response = $this->get('/scim/v2');
+
+        $response->assertStatus(200);
+        $response->assertJson([
+            'totalResults' => 200,
+            'itemsPerPage' => 10,
+            'startIndex' => 1,
+        ]);
+
+        $resources = $response->json('Resources');
+
+        $this->assertCount(10, $resources);
+        $this->assertEquals('User', $resources[0]['meta']['resourceType']);
+    }
+
+    public function testIndexSupportsStartIndexAcrossResources()
+    {
+        $response = $this->get('/scim/v2?startIndex=101&count=5');
+
+        $response->assertStatus(200);
+        $response->assertJson([
+            'totalResults' => 200,
+            'itemsPerPage' => 5,
+            'startIndex' => 101,
+        ]);
+
+        $resources = $response->json('Resources');
+
+        $this->assertCount(5, $resources);
+        $this->assertEquals('Group', $resources[0]['meta']['resourceType']);
+    }
+
+    public function testIndexReturnsUserAndGroup()
+    {
+        $response = $this->get('/scim/v2?startIndex=99&count=4');
+
+        $response->assertStatus(200);
+
+        $resources = collect($response->json('Resources'));
+
+        $this->assertSame([
+            'Group',
+            'User',
+        ], $resources->pluck('meta.resourceType')->unique()->sort()->values()->toArray());
+
+        $this->assertTrue(
+            $resources->contains(fn ($resource) =>
+                ($resource['meta']['resourceType'] ?? null) === 'User'
+                && ($resource['urn:ietf:params:scim:schemas:core:2.0:User']['userName'] ?? null) === 'boundary.user'
+            ),
+            'Boundary User not found in combined listing.'
+        );
+
+        $this->assertTrue(
+            $resources->contains(fn ($resource) =>
+                ($resource['meta']['resourceType'] ?? null) === 'Group'
+                && ($resource['urn:ietf:params:scim:schemas:core:2.0:Group']['displayName'] ?? null) === 'Boundary Group'
+            ),
+            'Boundary Group not found in combined listing.'
+        );
+    }
+
+    public function testIndexFilterRestrictsToUsers()
+    {
+        $response = $this->get('/scim/v2?filter=(meta.resourceType eq "User")');
+
+        $response->assertStatus(200);
+
+        $resources = collect($response->json('Resources'));
+
+        $this->assertNotEmpty($resources);
+        $this->assertSame(['User'], $resources->pluck('meta.resourceType')->unique()->values()->toArray());
+    }
+
+    public function testIndexFilterSupportsOrAcrossResourceTypes()
+    {
+        $responseFirstPage = $this->get('/scim/v2?count=10&filter=(meta.resourceType eq "User") or (meta.resourceType eq "Group")');
+
+        $responseFirstPage->assertStatus(200);
+
+        $resourcesFirstPage = collect($responseFirstPage->json('Resources'));
+
+        $this->assertTrue($resourcesFirstPage->contains(fn ($resource) => ($resource['meta']['resourceType'] ?? null) === 'User'));
+        $this->assertEmpty(array_diff($resourcesFirstPage->pluck('meta.resourceType')->unique()->values()->toArray(), ['User', 'Group']));
+
+        $responseSecondPage = $this->get('/scim/v2?startIndex=101&count=5&filter=(meta.resourceType eq "User") or (meta.resourceType eq "Group")');
+
+        $responseSecondPage->assertStatus(200);
+
+        $resourcesSecondPage = collect($responseSecondPage->json('Resources'));
+
+        $this->assertNotEmpty($resourcesSecondPage);
+        $this->assertEquals('Group', $resourcesSecondPage->first()['meta']['resourceType']);
+    }
+
+    public function testIndexRejectsCursorParameter()
+    {
+        $response = $this->get('/scim/v2?cursor=opaque');
+
+        $response->assertStatus(400);
+        $response->assertJson([
+            'scimType' => 'invalidCursor',
+            'status' => '400',
+        ]);
+    }
+
+    public function testPostSearchHonorsCountAndStartIndex()
+    {
+        $response = $this->postJson(
+            '/scim/v2/.search',
+            [
+                'schemas' => ['urn:ietf:params:scim:api:messages:2.0:SearchRequest'],
+                'count' => 5,
+                'startIndex' => 198,
+            ]
+        );
+
+        $response->assertStatus(200);
+        $response->assertJson([
+            'totalResults' => 200,
+            'startIndex' => 198,
+        ]);
+
+        $resources = $response->json('Resources');
+
+        $this->assertCount(3, $resources);
+        $this->assertSame(count($resources), $response->json('itemsPerPage'));
+        $this->assertEquals('Group', $resources[0]['meta']['resourceType']);
+    }
+}
diff --git a/tests/Model/Group.php b/tests/Model/Group.php
index 58732f2..f75a120 100644
--- a/tests/Model/Group.php
+++ b/tests/Model/Group.php
@@ -6,6 +6,8 @@
 
 class Group extends Model
 {
+    protected $guarded = [];
+
     public function members()
     {
         return $this
diff --git a/tests/Model/User.php b/tests/Model/User.php
index ff1c935..ea30a5d 100644
--- a/tests/Model/User.php
+++ b/tests/Model/User.php
@@ -6,10 +6,7 @@
 
 class User extends \Illuminate\Foundation\Auth\User
 {
-
-    protected $fillable = [
-        'roles',
-    ];
+    protected $guarded = [];
 
     protected $casts = [
         'active' => 'boolean',
diff --git a/tests/SchemaTest.php b/tests/SchemaTest.php
index f4f2e1e..5b86e56 100644
--- a/tests/SchemaTest.php
+++ b/tests/SchemaTest.php
@@ -64,6 +64,19 @@ public function testGet()
         $this->assertNotNull($activeAttribute, "Active attribute not found");
         $this->assertEquals('boolean', $activeAttribute['type'], "Active attribute is not of type boolean");
 
+        // Inspect the group schema to validate collection metadata for members.
+        $groupSchema = collect($jsonResponse['Resources'] ?? [])->firstWhere('id', 'urn:ietf:params:scim:schemas:core:2.0:Group');
+
+        $this->assertNotNull($groupSchema, 'Group schema not found');
+
+        $membersAttribute = collect($groupSchema['attributes'] ?? [])->firstWhere('name', 'members');
+
+        $this->assertNotNull($membersAttribute, 'members attribute missing from Group schema');
+        $this->assertSame('complex', $membersAttribute['type']);
+        $this->assertTrue($membersAttribute['multiValued']);
+        $this->assertSame('A list of members of the Group.', $membersAttribute['description']);
+        $this->assertNotEmpty($membersAttribute['subAttributes']);
+
     }
 
     public function getSchemaGenerator(){
diff --git a/tests/TestCase.php b/tests/TestCase.php
index a6c025a..4f8768e 100644
--- a/tests/TestCase.php
+++ b/tests/TestCase.php
@@ -63,6 +63,17 @@ protected function setUp(): void
         }
         $groups = factory(Group::class, 100)->create();
 
+        // Ensure deterministic boundary records for cross-resource pagination tests.
+        optional($users->sortBy('id')->last())->update([
+            'name' => 'boundary.user',
+            'formatted' => 'Boundary User',
+            'email' => 'boundary.user@example.test',
+        ]);
+
+        optional($groups->sortBy('id')->first())->update([
+            'displayName' => 'Boundary Group',
+        ]);
+
         $users->each(function ($user) use ($groups) {
             $user->groups()->attach(
                 $groups->random(rand(1, 3))->pluck('id')->toArray()