diff --git a/CHANGELOG.md b/CHANGELOG.md
index eda2b041..c45eb1ac 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -41,6 +41,7 @@ Inspired from [Keep a Changelog](https://keepachangelog.com/en/1.0.0/)
 - Added 404 response to `/_search/scroll` ([#749](https://github.com/opensearch-project/opensearch-api-specification/pull/749))
 - Added `node_failures` to `DELETE /_search/scroll` and `DELETE /_search/scroll/{scroll_id}` ([#749](https://github.com/opensearch-project/opensearch-api-specification/pull/749))
 - Added `POST /_plugins/_ml/_train/{algorithm_name}`, `_predict/{algorithm_name}/{model_id}`, and `_train_predict/{algorithm_name}` ([#755](https://github.com/opensearch-project/opensearch-api-specification/pull/755))
+- Added `PUT /_plugins/_ml/model_groups/{model_group_id}`, `GET /_plugins/_ml/model_groups/_search`, and `POST /_plugins/_ml/model_groups/_search` ([#760](https://github.com/opensearch-project/opensearch-api-specification/pull/760))
 
 ### Removed
 - Removed unsupported `_common.mapping:SourceField`'s `mode` field and associated `_common.mapping:SourceFieldMode` enum ([#652](https://github.com/opensearch-project/opensearch-api-specification/pull/652))
diff --git a/spec/namespaces/ml.yaml b/spec/namespaces/ml.yaml
index 25ec908b..53c47a6e 100644
--- a/spec/namespaces/ml.yaml
+++ b/spec/namespaces/ml.yaml
@@ -24,6 +24,18 @@ paths:
       responses:
         '200':
           $ref: '#/components/responses/ml.get_model_group@200'
+    put:
+      operationId: ml.update_model_group.0
+      x-operation-group: ml.update_model_group
+      x-version-added: '2.9'
+      description: Updates a model group.
+      parameters:
+        - $ref: '#/components/parameters/ml.update_model_group::path.model_group_id'
+      requestBody:
+        $ref: '#/components/requestBodies/ml.update_model_group'
+      responses:
+        '200':
+          $ref: '#/components/responses/ml.update_model_group@200'
     delete:
       operationId: ml.delete_model_group.0
       x-operation-group: ml.delete_model_group
@@ -33,6 +45,27 @@ paths:
       responses:
         '200':
           $ref: '#/components/responses/ml.delete_model_group@200'
+  /_plugins/_ml/model_groups/_search:
+    get:
+      operationId: ml.search_model_group.0
+      x-operation-group: ml.search_model_group
+      x-version-added: '2.9'
+      description: Searches for model groups.
+      requestBody:
+        $ref: '#/components/requestBodies/ml.search_model_group'
+      responses:
+        '200':
+          $ref: '#/components/responses/ml.search_model_group@200'
+    post:
+      operationId: ml.search_model_group.1
+      x-operation-group: ml.search_model_group
+      x-version-added: '2.9'
+      description: Searches for model groups.
+      requestBody:
+        $ref: '#/components/requestBodies/ml.search_model_group'
+      responses:
+        '200':
+          $ref: '#/components/responses/ml.search_model_group@200'
   /_plugins/_ml/models/_register:
     post:
       operationId: ml.register_model.0
@@ -207,6 +240,51 @@ components:
                 description: The add all backend roles.
             required:
               - name
+    ml.update_model_group:
+      content:
+        application/json:
+          schema:
+            type: object
+            properties:
+              name:
+                type: string
+                description: The model group name.
+              description:
+                type: string
+                description: The model group description.
+              add_all_backend_roles:
+                type: boolean
+                description: Whether to include all backend roles.
+              model_access_name:
+                type: string
+                description: The model access name
+              backend_roles:
+                type: array
+                items:
+                  type: string
+                description: The backend roles.
+              add_backend_roles:
+                type: array
+                items:
+                  type: string
+                description: The backend roles to add.
+    ml.search_model_group:
+      content:
+        application/json:
+          schema:
+            type: object
+            properties:
+              query:
+                $ref: '../schemas/ml._common.yaml#/components/schemas/Query'
+              size:
+                type: integer
+                format: int64
+                description: The number of model groups to return.
+              sort:
+                type: array
+                items:
+                  $ref: '../schemas/ml._common.yaml#/components/schemas/Sort'
+                description: The sort order.
     ml.register_model:
       content:
         application/json:
@@ -241,14 +319,16 @@ components:
             properties:
               query:
                 type: object
-                # TODO: Define the query schema
-                description: The query.
+                $ref: '../schemas/ml._common.yaml#/components/schemas/Query'
               size:
                 type: integer
+                format: int64
                 description: The number of models to return.
-            required:
-              - query
-              - size
+              sort:
+                type: array
+                items:
+                  $ref: '../schemas/ml._common.yaml#/components/schemas/Sort'
+                description: The sort order.
     ml.predict:
       content:
         application/json:
@@ -377,6 +457,16 @@ components:
         application/json:
           schema:
             $ref: '../schemas/ml._common.yaml#/components/schemas/ModelGroup'
+    ml.update_model_group@200:
+      content:
+        application/json:
+          schema:
+            $ref: '../schemas/ml._common.yaml#/components/schemas/UpdateModelGroupResponse'
+    ml.search_model_group@200:
+      content:
+        application/json:
+          schema:
+            $ref: '../schemas/ml._common.yaml#/components/schemas/SearchModelGroupsResponse'
     ml.delete_model_group@200:
       content:
         application/json:
@@ -483,6 +573,12 @@ components:
       required: true
       schema:
         type: string
+    ml.update_model_group::path.model_group_id:
+      name: model_group_id
+      in: path
+      required: true
+      schema:
+        type: string
     ml.delete_model_group::path.model_group_id:
       name: model_group_id
       in: path
diff --git a/spec/schemas/ml._common.yaml b/spec/schemas/ml._common.yaml
index 0c482a35..f140881c 100644
--- a/spec/schemas/ml._common.yaml
+++ b/spec/schemas/ml._common.yaml
@@ -7,6 +7,8 @@ paths: {}
 components:
   schemas:
     SearchModelsResponse:
+      $ref: '#/components/schemas/SearchResponse'
+    SearchResponse:
       type: object
       properties:
         took:
@@ -18,10 +20,10 @@ components:
         _shards:
           $ref: '_common.yaml#/components/schemas/ShardStatistics'
         hits:
-          $ref: '#/components/schemas/SearchModelsHits'
+          $ref: '#/components/schemas/SearchHits'
       required:
         - hits
-    SearchModelsHits:
+    SearchHits:
       type: object
       properties:
         total:
@@ -29,7 +31,7 @@ components:
         hits:
           type: array
           items:
-            $ref: '#/components/schemas/SearchModelsHitsHit'
+            $ref: '#/components/schemas/SearchHitsHit'
         max_score:
           type: number
           format: float
@@ -50,7 +52,7 @@ components:
       required:
         - relation
         - value
-    SearchModelsHitsHit:
+    SearchHitsHit:
       type: object
       properties:
         _version:
@@ -115,6 +117,7 @@ components:
             - PARTIALLY_DEPLOYED
             - REGISTERED
             - REGISTERING
+            - UNDEPLOYED
         model_content_size_in_bytes:
           type: integer
           format: int64
@@ -171,6 +174,23 @@ components:
         url:
           type: string
           description: The model URL.
+        backend_roles:
+          type: array
+          items:
+            type: string
+          description: The backend roles.
+        owner:
+          $ref: '#/components/schemas/Owner'
+        access:
+          type: string
+          description: The model group access.
+          enum:
+            - private
+            - public
+            - restricted
+        latest_version:
+          type: integer
+          description: The latest version.
     ModelConfig:
       type: object
       properties:
@@ -329,6 +349,14 @@ components:
       properties:
         bool:
           $ref: '#/components/schemas/BoolQuery'
+        match_all:
+          $ref: '#/components/schemas/MatchAllQuery'
+        term:
+          $ref: '#/components/schemas/Term'
+    MatchAllQuery:
+      type: object
+      description: The match all query.
+      properties: {}
     BoolQuery:
       type: object
       description: The Boolean query.
@@ -338,12 +366,35 @@ components:
           description: Filter query that appears in matching documents.
           items:
             $ref: '#/components/schemas/Filter'
+        must:
+          type: array
+          description: Query that must appears in matching documents
+          items:
+            $ref: '#/components/schemas/Filter'
+        must_not:
+          description: Query that must not appears in matching documents.
+          $ref: '#/components/schemas/Filter'
+        should:
+          type: array
+          description: Query that should appear in matching documents.
+          items:
+            $ref: '#/components/schemas/Filter'
     Filter:
       type: object
       description: The filter element.
       properties:
         range:
           $ref: '#/components/schemas/Range'
+        nested:
+          $ref: '#/components/schemas/Nested'
+        exists:
+          $ref: '#/components/schemas/Exists'
+        term:
+          $ref: '#/components/schemas/Term'
+        terms:
+          $ref: '#/components/schemas/Term'
+        match:
+          $ref: '#/components/schemas/Match'
     Range:
       type: object
       description: The filter range.
@@ -370,6 +421,150 @@ components:
         lt:
           type: number
           description: Less than.
+    Term:
+      type: object
+      description: Term to match the query.
+      properties:
+        algorithm:
+          $ref: '#/components/schemas/Algorithm'
+        _id:
+          type: array
+          items:
+            $ref: '_common.yaml#/components/schemas/Id'
+        model_id:
+          $ref: '_common.yaml#/components/schemas/Name'
+        owner.name.keyword:
+          $ref: '#/components/schemas/OwnerNameKeyword'
+    Algorithm:
+      type: object
+      description: The algorithm.
+      properties:
+        value:
+          type: string
+          description: The function name.
+          enum:
+            - AD_LIBSVM
+            - AGENT
+            - ANOMALY_LOCALIZATION
+            - BATCH_RCF
+            - CONNECTOR
+            - FIT_RCF
+            - KMEANS
+            - LINEAR_REGRESSION
+            - LOCAL_SAMPLE_CALCULATOR
+            - LOGISTIC_REGRESSION
+            - METRICS_CORRELATION
+            - QUESTION_ANSWERING
+            - RCF_SUMMARIZE
+            - REMOTE
+            - SAMPLE_ALGO
+            - SPARSE_ENCODING
+            - SPARSE_TOKENIZE
+            - TEXT_EMBEDDING
+            - TEXT_SIMILARITY
+    OwnerNameKeyword:
+      type: object
+      description: The owner name keyword.
+      properties:
+        value:
+          $ref: '_common.yaml#/components/schemas/FieldValue'
+        boost:
+          type: number
+          description: Adjust the relevance score of a match.
+    Nested:
+      type: object
+      description: The nested filter.
+      properties:
+        query:
+          $ref: '#/components/schemas/Query'
+        path:
+          $ref: '_common.yaml#/components/schemas/Field'
+        ignore_unmapped:
+          type: boolean
+          description: Whether to ignore unmapped fields.
+        score_mode:
+          type: string
+          description: The score mode.
+          enum:
+            - avg
+            - max
+            - min
+            - none
+            - sum
+        boost:
+          type: number
+          description: Adjust the relevance score of a match.
+    Exists:
+      type: object
+      description: The exists filter.
+      properties:
+        field:
+          $ref: '_common.yaml#/components/schemas/Field'
+    Sort:
+      type: object
+      description: Sort query.
+      properties:
+        algorithm:
+          $ref: '#/components/schemas/SortOrder'
+        auto_redeploy_retry_times:
+          $ref: '#/components/schemas/SortOrder'
+        chunk_number:
+          $ref: '#/components/schemas/SortOrder'
+        created_time:
+          $ref: '#/components/schemas/SortOrder'
+        current_worker_node_count:
+          $ref: '#/components/schemas/SortOrder'
+        deploy_to_all_nodes:
+          $ref: '#/components/schemas/SortOrder'
+        is_hidden:
+          $ref: '#/components/schemas/SortOrder'
+        last_registered_time:
+          $ref: '#/components/schemas/SortOrder'
+        last_updated_time:
+          $ref: '#/components/schemas/SortOrder'
+        model_content_hash_value:
+          $ref: '#/components/schemas/SortOrder'
+        model_content_size_in_bytes:
+          $ref: '#/components/schemas/SortOrder'
+        model_format:
+          $ref: '#/components/schemas/SortOrder'
+        model_group_id:
+          $ref: '#/components/schemas/SortOrder'
+        model_state:
+          $ref: '#/components/schemas/SortOrder'
+        model_version:
+          $ref: '#/components/schemas/SortOrder'
+        planning_worker_nodes:
+          $ref: '#/components/schemas/SortOrder'
+        planning_worker_node_count:
+          $ref: '#/components/schemas/SortOrder'
+        total_chunks:
+          $ref: '#/components/schemas/SortOrder'
+        _index:
+          $ref: '#/components/schemas/SortOrder'
+        _id:
+          $ref: '#/components/schemas/SortOrder'
+        _seq_no:
+          $ref: '#/components/schemas/SortOrder'
+        _score:
+          $ref: '#/components/schemas/SortOrder'
+    SortOrder:
+      type: object
+      description: The order of the sort.
+      properties:
+        order:
+          type: string
+          description: The order.
+          enum:
+            - asc
+            - desc
+    Match:
+      type: object
+      description: Match query.
+      properties:
+        description:
+          type: string
+          description: The description.
     TrainParameters:
       type: object
       properties:
@@ -430,9 +625,15 @@ components:
         description:
           type: string
           description: The model group description.
+        owner:
+          $ref: '#/components/schemas/Owner'
         access:
           type: string
           description: The model group access.
+          enum:
+            - private
+            - public
+            - restricted
         created_time:
           type: integer
           format: int64
@@ -444,6 +645,39 @@ components:
         - description
         - latest_version
         - name
+    Owner:
+      type: object
+      properties:
+        name:
+          $ref: '_common.yaml#/components/schemas/Name'
+        backend_roles:
+          type: array
+          items:
+            type: string
+          description: The backend roles.
+        roles:
+          type: array
+          items:
+            type: string
+          description: The roles.
+        custom_attribute_names:
+          type: array
+          items:
+            type: string
+          description: The custom attribute names.
+        user_requested_tenant:
+          type: ['null', string]
+          description: The user requested tenant.
+      required:
+        - name
+    UpdateModelGroupResponse:
+      type: object
+      properties:
+        status:
+          type: string
+          description: The status.
+    SearchModelGroupsResponse:
+      $ref: '#/components/schemas/SearchResponse'
     Task:
       type: object
       properties:
diff --git a/tests/plugins/ml/ml/model_groups/search.yaml b/tests/plugins/ml/ml/model_groups/search.yaml
new file mode 100644
index 00000000..717b87a7
--- /dev/null
+++ b/tests/plugins/ml/ml/model_groups/search.yaml
@@ -0,0 +1,52 @@
+$schema: ../../../../../json_schemas/test_story.schema.yaml
+
+description: Test the search of model groups.
+version: '>= 2.9'
+prologues:
+  - path: /_plugins/_ml/model_groups/_register
+    id: create_model_group
+    method: POST
+    request:
+      payload:
+        name: NLP_Group
+        description: Model group for NLP models.
+    output:
+      test_model_group_id: payload.model_group_id
+epilogues:
+  - path: /_plugins/_ml/model_groups/{model_group_id}
+    method: DELETE
+    status: [200, 404]
+    parameters:
+      model_group_id: ${create_model_group.test_model_group_id}
+chapters:
+  - synopsis: Search model group.
+    path: /_plugins/_ml/model_groups/_search
+    method: GET
+    request:
+      payload:
+        query:
+          match_all: {}
+        size: 1000
+    response:
+      status: 200
+      payload:
+        hits:
+          hits:
+            - _score: 1
+  - synopsis: Search model group with a model group ID.
+    path: /_plugins/_ml/model_groups/_search
+    method: POST
+    request:
+      payload:
+        query:
+          bool:
+            must:
+              - terms:
+                  _id: 
+                    - ${create_model_group.test_model_group_id}
+    response:
+      status: 200
+      payload:
+        hits:
+          hits:
+            - _score: 1
diff --git a/tests/plugins/ml/ml/model_groups/update.yaml b/tests/plugins/ml/ml/model_groups/update.yaml
new file mode 100644
index 00000000..e9ef14a3
--- /dev/null
+++ b/tests/plugins/ml/ml/model_groups/update.yaml
@@ -0,0 +1,36 @@
+$schema: ../../../../../json_schemas/test_story.schema.yaml
+
+description: Test the creation of model groups.
+version: '>= 2.9'
+prologues:
+  - path: /_plugins/_ml/model_groups/_register
+    id: create_model_group
+    method: POST
+    request:
+      payload:
+        name: NLP_Group
+        description: Model group for NLP models.
+    output:
+      test_model_group_id: payload.model_group_id
+  - path: /_plugins/_ml/model_groups/{model_group_id}
+    method: GET
+    parameters:
+      model_group_id: ${create_model_group.test_model_group_id}
+    status: [200, 404]
+epilogues:
+  - path: /_plugins/_ml/model_groups/{model_group_id}
+    method: DELETE
+    status: [200, 404]
+    parameters:
+      model_group_id: ${create_model_group.test_model_group_id}
+chapters:
+  - synopsis: Update model group.
+    path: /_plugins/_ml/model_groups/{model_group_id}
+    method: PUT
+    parameters:
+      model_group_id: ${create_model_group.test_model_group_id}
+    request:
+      payload:
+        description: This is the updated description.
+    response:
+      status: 200