diff --git a/google-cloud-spanner/lib/google/cloud/spanner/commit.rb b/google-cloud-spanner/lib/google/cloud/spanner/commit.rb
index 29295180..319c391d 100644
--- a/google-cloud-spanner/lib/google/cloud/spanner/commit.rb
+++ b/google-cloud-spanner/lib/google/cloud/spanner/commit.rb
@@ -280,6 +280,124 @@ def delete table, keys = []
           keys
         end
 
+        ##
+        # Sends a message to a queue.
+        #
+        # All changes are accumulated in memory until the block passed to
+        # {Client#commit} completes.
+        #
+        # @param [String] queue The name of the queue.
+        # @param [Object, Array<Object>] key A single key or array of composite key parts for the message.
+        # @param [String, IO, StringIO, Hash, Google::Protobuf::MessageExts] payload
+        #   The message payload. It is converted the same way as column values
+        #   (see {#upsert}), so its type must match the queue's payload column,
+        #   such as a `String` for `STRING` or a `StringIO` for `BYTES`:
+        #   * `String` - Sent as text.
+        #   * `IO`, `StringIO`, `File` - Sent as bytes (Base64-encoded). Ruby has
+        #     no bytes type, so wrap binary data in a `StringIO`.
+        #   * `Hash` - Serialized to a JSON string.
+        #   * `Google::Protobuf::MessageExts` - Serialized and Base64-encoded.
+        # @param [Time, nil] deliver_time The time at which Spanner begins
+        #   trying to deliver the message. Optional. If not set, the message is
+        #   delivered immediately. A time in the past is replaced with a time
+        #   closer to the current time.
+        #
+        # @return [Object, Array<Object>] The key of the message.
+        #
+        # @raise [ArgumentError] If the payload type is unsupported.
+        #
+        # @example
+        #   require "google/cloud/spanner"
+        #
+        #   spanner = Google::Cloud::Spanner.new
+        #
+        #   db = spanner.client "my-instance", "my-database"
+        #
+        #   # OrderQueue has a STRING(MAX) payload column.
+        #   db.commit do |c|
+        #     c.send_message "OrderQueue", 101, "Order payload"
+        #   end
+        #
+        # @example Send binary data to a queue with a BYTES payload column
+        #   require "google/cloud/spanner"
+        #
+        #   spanner = Google::Cloud::Spanner.new
+        #
+        #   db = spanner.client "my-instance", "my-database"
+        #
+        #   db.commit do |c|
+        #     c.send_message "LabelQueue", 101, StringIO.new(File.binread("label.png"))
+        #   end
+        #
+        # @example Deliver the message in five minutes
+        #   require "google/cloud/spanner"
+        #
+        #   spanner = Google::Cloud::Spanner.new
+        #
+        #   db = spanner.client "my-instance", "my-database"
+        #
+        #   db.commit do |c|
+        #     c.send_message "OrderQueue", 101, "Order payload",
+        #                    deliver_time: Time.now + 300
+        #   end
+        #
+        def send_message queue, key, payload, deliver_time: nil
+          send_mutation = V1::Mutation::Send.new(
+            queue: queue,
+            key: key_list_value(key),
+            payload: Convert.object_to_grpc_value(payload),
+            deliver_time: Convert.time_to_timestamp(deliver_time)
+          )
+          @mutations += [V1::Mutation.new(send: send_mutation)]
+          key
+        end
+
+        ##
+        # Acknowledges a message in a queue, which removes it from the queue.
+        #
+        # All changes are accumulated in memory until the block passed to
+        # {Client#commit} completes.
+        #
+        # @param [String] queue The name of the queue.
+        # @param [Object, Array<Object>] key A single key or array of composite key parts to match.
+        # @param [Boolean] ignore_not_found If `true`, the ack succeeds even if
+        #   the message doesn't exist. Optional. The default is `false`, which
+        #   fails the commit with `NOT_FOUND` when the message doesn't exist.
+        #
+        # @return [Object, Array<Object>] The key of the message.
+        #
+        # @example
+        #   require "google/cloud/spanner"
+        #
+        #   spanner = Google::Cloud::Spanner.new
+        #
+        #   db = spanner.client "my-instance", "my-database"
+        #
+        #   db.commit do |c|
+        #     c.ack_message "OrderQueue", 101
+        #   end
+        #
+        # @example Ack a message whether or not it exists
+        #   require "google/cloud/spanner"
+        #
+        #   spanner = Google::Cloud::Spanner.new
+        #
+        #   db = spanner.client "my-instance", "my-database"
+        #
+        #   db.commit do |c|
+        #     c.ack_message "OrderQueue", 101, ignore_not_found: true
+        #   end
+        #
+        def ack_message queue, key, ignore_not_found: false
+          ack_mutation = V1::Mutation::Ack.new(
+            queue: queue,
+            key: key_list_value(key),
+            ignore_not_found: ignore_not_found
+          )
+          @mutations += [V1::Mutation.new(ack: ack_mutation)]
+          key
+        end
+
         # Return the current mutations added to this `Spanner::Commit` object.
         # @private
         # @return [Array<Google::Cloud::Spanner::V1::Mutation>]
@@ -325,6 +443,21 @@ def mutations_from_rows table, rows, type
           rows
         end
 
+        ##
+        # @private
+        # Generates a `ListValue` protobuf containing gRPC values for the given primary key.
+        #
+        # @param [Object, Array<Object>] key A scalar key, or an array of a composite key's parts.
+        # @return [Google::Protobuf::ListValue]
+        #
+        def key_list_value key
+          key = [key] unless key.is_a? Array
+          key_list = key.map do |k|
+            Convert.object_to_grpc_value k
+          end
+          Google::Protobuf::ListValue.new values: key_list
+        end
+
         def key_set keys
           return V1::KeySet.new all: true if keys.nil?
           keys = [keys] unless keys.is_a? Array
diff --git a/google-cloud-spanner/test/google/cloud/spanner/commit_queues_test.rb b/google-cloud-spanner/test/google/cloud/spanner/commit_queues_test.rb
new file mode 100644
index 00000000..fae81e2a
--- /dev/null
+++ b/google-cloud-spanner/test/google/cloud/spanner/commit_queues_test.rb
@@ -0,0 +1,123 @@
+# Copyright 2026 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     https://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+require "helper"
+
+describe Google::Cloud::Spanner::Commit, :queues, :mock_spanner do
+  let(:commit) { Google::Cloud::Spanner::Commit.new }
+  let(:deliver_time) { Time.now + 300 }
+
+  it "builds a send mutation with scalar key" do
+    commit.send_message "TestQueue", 2, "Hello, Queues!"
+
+    assert_equal 1, commit.mutations.count
+    mutation = commit.mutations.first
+
+    assert mutation["send"]
+    assert_equal "TestQueue", mutation["send"].queue
+    assert_equal Google::Cloud::Spanner::Convert.object_to_grpc_value([2]).list_value, mutation["send"].key
+    assert_equal Google::Cloud::Spanner::Convert.object_to_grpc_value("Hello, Queues!"), mutation["send"].payload
+    assert_nil mutation["send"].deliver_time
+  end
+
+  it "builds a send mutation with composite key" do
+    commit.send_message "TestQueue", ["tenant1", 2], "Hello, Queues!"
+
+    assert_equal 1, commit.mutations.count
+    mutation = commit.mutations.first
+
+    assert mutation["send"]
+    assert_equal "TestQueue", mutation["send"].queue
+    assert_equal Google::Cloud::Spanner::Convert.object_to_grpc_value(["tenant1", 2]).list_value, mutation["send"].key
+    assert_equal Google::Cloud::Spanner::Convert.object_to_grpc_value("Hello, Queues!"), mutation["send"].payload
+    assert_nil mutation["send"].deliver_time
+  end
+
+  it "encodes StringIO payloads as Base64" do
+    raw_bytes = "\x00\x01\x02\xFF".b
+    commit.send_message "TestQueue", 1, StringIO.new(raw_bytes)
+
+    assert_equal 1, commit.mutations.count
+    assert_equal Base64.strict_encode64(raw_bytes), commit.mutations.first["send"].payload.string_value
+  end
+
+  it "encodes Hash payload as JSON string" do
+    hash_payload = { "event" => "user_created", "status" => "active" }
+
+    commit.send_message "TestQueue", 1, hash_payload
+
+    assert_equal 1, commit.mutations.count
+    mutation = commit.mutations.first
+
+    assert_equal hash_payload.to_json, mutation["send"].payload.string_value
+  end
+
+  it "raises ArgumentError for unsupported payload types" do
+    assert_raises ArgumentError do
+      commit.send_message "TestQueue", 1, Object.new
+    end
+  end
+
+  it "sets deliver_time" do
+    commit.send_message "TestQueue", 1, "payload", deliver_time: deliver_time
+
+    expected = Google::Cloud::Spanner::Convert.time_to_timestamp deliver_time
+    assert_equal expected, commit.mutations.first["send"].deliver_time
+  end
+
+  it "raises ArgumentError for an unknown send_message keyword" do
+    assert_raises(ArgumentError) { commit.send_message "TestQueue", 1, "payload", deliver_at: deliver_time }
+    assert_empty commit.mutations
+  end
+
+  it "returns the key from send_message" do
+    assert_equal 2, commit.send_message("TestQueue", 2, "payload")
+    assert_equal ["tenant1", 2], commit.send_message("TestQueue", ["tenant1", 2], "payload")
+  end
+
+  it "builds an ack mutation with scalar and composite keys" do
+    commit.ack_message "TestQueue", 2
+    commit.ack_message "TestQueue", ["tenant1", 2]
+
+    assert_equal 2, commit.mutations.count
+    m1 = commit.mutations[0]
+    m2 = commit.mutations[1]
+
+    assert m1.ack
+    assert_equal "TestQueue", m1.ack.queue
+    assert_equal Google::Cloud::Spanner::Convert.object_to_grpc_value([2]).list_value, m1.ack.key
+    assert_equal false, m1.ack.ignore_not_found
+
+    assert m2.ack
+    assert_equal "TestQueue", m2.ack.queue
+    assert_equal Google::Cloud::Spanner::Convert.object_to_grpc_value(["tenant1", 2]).list_value, m2.ack.key
+    assert_equal false, m2.ack.ignore_not_found
+  end
+
+  it "sets ignore_not_found" do
+    commit.ack_message "TestQueue", 1, ignore_not_found: true
+
+    assert_equal true, commit.mutations.first.ack.ignore_not_found
+  end
+
+  it "raises ArgumentError for an unknown ack_message keyword" do
+    assert_raises(ArgumentError) { commit.ack_message "TestQueue", 1, ignore_missing: true }
+    assert_empty commit.mutations
+  end
+
+  it "returns the key from ack_message" do
+    assert_equal 2, commit.ack_message("TestQueue", 2)
+    assert_equal ["tenant1", 2], commit.ack_message("TestQueue", ["tenant1", 2])
+  end
+end