diff --git a/Manifest.txt b/Manifest.txt
index 21c55f70e4b4..08a6cb8641df 100644
--- a/Manifest.txt
+++ b/Manifest.txt
@@ -12,6 +12,7 @@ lib/gcloud/datastore/connection.rb
 lib/gcloud/datastore/credentials.rb
 lib/gcloud/datastore/dataset.rb
 lib/gcloud/datastore/entity.rb
+lib/gcloud/datastore/errors.rb
 lib/gcloud/datastore/key.rb
 lib/gcloud/datastore/list.rb
 lib/gcloud/datastore/proto.rb
diff --git a/gcloud.gemspec b/gcloud.gemspec
index 2a0b6c7e8af5..d0c61e1a91f8 100644
--- a/gcloud.gemspec
+++ b/gcloud.gemspec
@@ -1,18 +1,18 @@
 # -*- encoding: utf-8 -*-
-# stub: gcloud 0.0.1.20141114161251 ruby lib
+# stub: gcloud 0.0.1.20141119145908 ruby lib
 
 Gem::Specification.new do |s|
   s.name = "gcloud"
-  s.version = "0.0.1.20141114161251"
+  s.version = "0.0.1.20141119145908"
 
   s.required_rubygems_version = Gem::Requirement.new(">= 0") if s.respond_to? :required_rubygems_version=
   s.require_paths = ["lib"]
   s.authors = ["Silvano Luciani", "Mike Moore"]
-  s.date = "2014-11-14"
+  s.date = "2014-11-19"
   s.description = "Gcloud is the official library for interacting with Google Cloud."
   s.email = ["silvano@google.com", "mike@blowmage.com"]
   s.extra_rdoc_files = ["CHANGELOG.md", "CONTRIBUTING.md", "Manifest.txt", "README.md"]
-  s.files = [".gemtest", ".rubocop.yml", "CHANGELOG.md", "CONTRIBUTING.md", "LICENSE", "Manifest.txt", "README.md", "Rakefile", "gcloud.gemspec", "lib/gcloud.rb", "lib/gcloud/datastore.rb", "lib/gcloud/datastore/connection.rb", "lib/gcloud/datastore/credentials.rb", "lib/gcloud/datastore/dataset.rb", "lib/gcloud/datastore/entity.rb", "lib/gcloud/datastore/key.rb", "lib/gcloud/datastore/list.rb", "lib/gcloud/datastore/proto.rb", "lib/gcloud/datastore/query.rb", "lib/gcloud/datastore/transaction.rb", "lib/gcloud/proto/datastore_v1.pb.rb", "lib/gcloud/version.rb", "rakelib/console.rake", "rakelib/proto.rake", "rakelib/rubocop.rake", "rakelib/test.rake", "regression/data/index.yaml", "regression/datastore/test_datastore.rb", "regression/datastore_helper.rb", "test/gcloud/datastore/proto/test_cursor.rb", "test/gcloud/datastore/proto/test_direction.rb", "test/gcloud/datastore/proto/test_operator.rb", "test/gcloud/datastore/proto/test_value.rb", "test/gcloud/datastore/test_connection.rb", "test/gcloud/datastore/test_credentials.rb", "test/gcloud/datastore/test_dataset.rb", "test/gcloud/datastore/test_entity.rb", "test/gcloud/datastore/test_key.rb", "test/gcloud/datastore/test_query.rb", "test/gcloud/datastore/test_transaction.rb", "test/gcloud/test_version.rb", "test/helper.rb"]
+  s.files = [".gemtest", ".rubocop.yml", "CHANGELOG.md", "CONTRIBUTING.md", "LICENSE", "Manifest.txt", "README.md", "Rakefile", "gcloud.gemspec", "lib/gcloud.rb", "lib/gcloud/datastore.rb", "lib/gcloud/datastore/connection.rb", "lib/gcloud/datastore/credentials.rb", "lib/gcloud/datastore/dataset.rb", "lib/gcloud/datastore/entity.rb", "lib/gcloud/datastore/errors.rb", "lib/gcloud/datastore/key.rb", "lib/gcloud/datastore/list.rb", "lib/gcloud/datastore/proto.rb", "lib/gcloud/datastore/query.rb", "lib/gcloud/datastore/transaction.rb", "lib/gcloud/proto/datastore_v1.pb.rb", "lib/gcloud/version.rb", "rakelib/console.rake", "rakelib/proto.rake", "rakelib/rubocop.rake", "rakelib/test.rake", "regression/data/index.yaml", "regression/datastore/test_datastore.rb", "regression/datastore_helper.rb", "test/gcloud/datastore/proto/test_cursor.rb", "test/gcloud/datastore/proto/test_direction.rb", "test/gcloud/datastore/proto/test_operator.rb", "test/gcloud/datastore/proto/test_value.rb", "test/gcloud/datastore/test_connection.rb", "test/gcloud/datastore/test_credentials.rb", "test/gcloud/datastore/test_dataset.rb", "test/gcloud/datastore/test_entity.rb", "test/gcloud/datastore/test_key.rb", "test/gcloud/datastore/test_query.rb", "test/gcloud/datastore/test_transaction.rb", "test/gcloud/test_version.rb", "test/helper.rb"]
   s.homepage = "http://googlecloudplatform.github.io/gcloud-ruby/"
   s.licenses = ["Apache-2.0"]
   s.rdoc_options = ["--main", "README.md", "--exclude", "lib/gcloud/proto/"]
diff --git a/lib/gcloud.rb b/lib/gcloud.rb
index 9a006a6d23b9..be1cc8421c2f 100644
--- a/lib/gcloud.rb
+++ b/lib/gcloud.rb
@@ -1 +1,8 @@
 require "gcloud/version"
+
+module Gcloud
+  ##
+  # Standard Gcloud exception class.
+  class Error < StandardError
+  end
+end
diff --git a/lib/gcloud/datastore.rb b/lib/gcloud/datastore.rb
index e17a256c1e59..22bb1906c287 100644
--- a/lib/gcloud/datastore.rb
+++ b/lib/gcloud/datastore.rb
@@ -13,6 +13,7 @@
 # limitations under the License.
 
 require "gcloud"
+require "gcloud/datastore/errors"
 require "gcloud/datastore/dataset"
 require "gcloud/datastore/transaction"
 require "gcloud/datastore/credentials"
diff --git a/lib/gcloud/datastore/connection.rb b/lib/gcloud/datastore/connection.rb
index 44c0052a8514..05aff662ea81 100644
--- a/lib/gcloud/datastore/connection.rb
+++ b/lib/gcloud/datastore/connection.rb
@@ -117,8 +117,8 @@ def rpc proto_method, proto_request
           @credentials.sign_http_request req
         end
 
-        # TODO: Raise a proper error if the response is not 2xx (success)
-        fail response.inspect unless response.success?
+        fail ConnectionError, proto_method, response unless response.success?
+
         response.body
       end
 
diff --git a/lib/gcloud/datastore/credentials.rb b/lib/gcloud/datastore/credentials.rb
index 118d10b251f1..0a5dc99c85a9 100644
--- a/lib/gcloud/datastore/credentials.rb
+++ b/lib/gcloud/datastore/credentials.rb
@@ -29,9 +29,9 @@ class Credentials # :nodoc:
 
       def initialize keyfile
         if keyfile.nil?
-          fail "You must provide a keyfile to connect with."
+          fail KeyfileError, "You must provide a keyfile to connect with."
         elsif !File.exist?(keyfile)
-          fail "The keyfile '#{keyfile}' is not a valid file."
+          fail KeyfileError, "The keyfile '#{keyfile}' is not a valid file."
         end
 
         options = JSON.parse(File.read(keyfile))
diff --git a/lib/gcloud/datastore/dataset.rb b/lib/gcloud/datastore/dataset.rb
index 5c95c746cff7..a32d9de7b8dc 100644
--- a/lib/gcloud/datastore/dataset.rb
+++ b/lib/gcloud/datastore/dataset.rb
@@ -46,7 +46,9 @@ def dataset_id
       #   empty_key = Gcloud::Datastore::Key.new "Task"
       #   task_keys = conn.allocate_ids empty_key, 5
       def allocate_ids incomplete_key, count = 1
-        fail "An incomplete key must be provided." if incomplete_key.complete?
+        if incomplete_key.complete?
+          fail Gcloud::Datastore::Error, "An incomplete key must be provided."
+        end
 
         incomplete_keys = count.times.map { incomplete_key.to_proto }
         response = connection.allocate_ids(*incomplete_keys)
@@ -134,9 +136,9 @@ def transaction
         begin
           yield tx
           tx.commit
-        rescue
+        rescue => e
           tx.rollback
-          raise "Transaction failed to commit."
+          raise TransactionError.new("Transaction failed to commit.", e)
         end
       end
 
diff --git a/lib/gcloud/datastore/errors.rb b/lib/gcloud/datastore/errors.rb
new file mode 100644
index 000000000000..e4beebf48939
--- /dev/null
+++ b/lib/gcloud/datastore/errors.rb
@@ -0,0 +1,55 @@
+# Copyright 2014 Google Inc. All rights reserved.
+#
+# 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
+#
+#     http://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 "gcloud"
+
+module Gcloud
+  module Datastore
+    ##
+    # Standard Datastore exception class.
+    class Error < Gcloud::Error
+    end
+
+    ##
+    # Raised when a keyfile is not correct.
+    class KeyfileError < Gcloud::Datastore::Error
+    end
+
+    ##
+    # Raised when an API call is not successful.
+    class ApiError < Gcloud::Datastore::Error
+      ##
+      # The response object of the failed HTTP request.
+      attr_reader :response
+
+      def initialize method, response = nil
+        super "API call to #{method} was not successful"
+        @response = response
+      end
+    end
+
+    ##
+    # General error for Transaction problems.
+    class TransactionError < Gcloud::Datastore::Error
+      ##
+      # An error that occurred within the transaction. (optional)
+      attr_reader :inner
+
+      def initialize message, inner = nil
+        super message
+        @inner = inner
+      end
+    end
+  end
+end
diff --git a/lib/gcloud/datastore/transaction.rb b/lib/gcloud/datastore/transaction.rb
index 4ff1889d1287..de75676c40d3 100644
--- a/lib/gcloud/datastore/transaction.rb
+++ b/lib/gcloud/datastore/transaction.rb
@@ -45,14 +45,16 @@ def delete *entities
       end
 
       def start
-        fail "Transaction already opened" unless @id.nil?
+        fail TransactionError, "Transaction already opened." unless @id.nil?
 
         response = connection.begin_transaction
         @id = response.transaction
       end
 
       def commit
-        fail "Cannot commit when not in a transaction" if @id.nil?
+        if @id.nil?
+          fail TransactionError, "Cannot commit when not in a transaction."
+        end
 
         response = connection.commit shared_mutation, @id
         auto_id_assign_ids response.mutation_result.insert_auto_id_key
@@ -60,7 +62,9 @@ def commit
       end
 
       def rollback
-        fail "Cannot rollback when not in a transaction" if @id.nil?
+        if @id.nil?
+          fail TransactionError, "Cannot rollback when not in a transaction."
+        end
 
         connection.rollback @id
         true
diff --git a/test/gcloud/datastore/test_dataset.rb b/test/gcloud/datastore/test_dataset.rb
index 865febe7671a..9797aad44070 100644
--- a/test/gcloud/datastore/test_dataset.rb
+++ b/test/gcloud/datastore/test_dataset.rb
@@ -86,7 +86,7 @@
   it "allocate_ids raises when not given an incomplete key" do
     complete_key = Gcloud::Datastore::Key.new "ds-test", 789
     complete_key.must_be :complete?
-    assert_raises RuntimeError do
+    assert_raises Gcloud::Datastore::Error do
       dataset.allocate_ids complete_key
     end
   end
@@ -208,4 +208,21 @@
       tx.save entity
     end
   end
+
+  it "transaction will wrap errors in TransactionError" do
+    dataset.connection.expect :begin_transaction,
+                              begin_transaction_response
+    dataset.connection.expect :rollback, nil, [String]
+
+    error = assert_raises Gcloud::Datastore::TransactionError do
+      dataset.transaction do |tx|
+        fail "This error should be wrapped by TransactionError."
+      end
+    end
+
+    error.wont_be :nil?
+    error.message.must_equal "Transaction failed to commit."
+    error.inner.wont_be :nil?
+    error.inner.message.must_equal "This error should be wrapped by TransactionError."
+  end
 end
diff --git a/test/gcloud/datastore/test_entity.rb b/test/gcloud/datastore/test_entity.rb
index 8c706febedb0..ca4f5a18bffb 100644
--- a/test/gcloud/datastore/test_entity.rb
+++ b/test/gcloud/datastore/test_entity.rb
@@ -13,7 +13,7 @@
 # limitations under the License.
 
 require "helper"
-require "gcloud/datastore/entity"
+require "gcloud/datastore"
 
 describe Gcloud::Datastore::Entity do
 
diff --git a/test/gcloud/datastore/test_key.rb b/test/gcloud/datastore/test_key.rb
index 0d1edb521738..c27ba1d59396 100644
--- a/test/gcloud/datastore/test_key.rb
+++ b/test/gcloud/datastore/test_key.rb
@@ -13,7 +13,7 @@
 # limitations under the License.
 
 require "helper"
-require "gcloud/datastore/key"
+require "gcloud/datastore"
 
 describe Gcloud::Datastore::Key do
 
diff --git a/test/gcloud/datastore/test_query.rb b/test/gcloud/datastore/test_query.rb
index 015c52b57e5a..d6c6b626bf12 100644
--- a/test/gcloud/datastore/test_query.rb
+++ b/test/gcloud/datastore/test_query.rb
@@ -13,7 +13,7 @@
 # limitations under the License.
 
 require "helper"
-require "gcloud/datastore/query"
+require "gcloud/datastore"
 
 describe Gcloud::Datastore::Query do
   it "can query on kind" do
diff --git a/test/gcloud/datastore/test_transaction.rb b/test/gcloud/datastore/test_transaction.rb
index 82de92719828..48f8d193a20b 100644
--- a/test/gcloud/datastore/test_transaction.rb
+++ b/test/gcloud/datastore/test_transaction.rb
@@ -81,4 +81,41 @@
     transaction.save entity
     transaction.rollback
   end
+
+  describe "error handling" do
+    it "start will raise if transaction is already open" do
+      transaction.id.wont_be :nil?
+      error = assert_raises Gcloud::Datastore::TransactionError do
+        transaction.start
+      end
+      error.wont_be :nil?
+      error.message.must_equal "Transaction already opened."
+    end
+
+    it "commit will raise if transaction is not open" do
+      transaction.connection.expect :begin_transaction, begin_transaction_response
+
+      transaction.id.wont_be :nil?
+      transaction.reset!
+      transaction.id.must_be :nil?
+      error = assert_raises Gcloud::Datastore::TransactionError do
+        transaction.commit
+      end
+      error.wont_be :nil?
+      error.message.must_equal "Cannot commit when not in a transaction."
+    end
+
+    it "transaction will raise if transaction is not open" do
+      transaction.connection.expect :begin_transaction, begin_transaction_response
+
+      transaction.id.wont_be :nil?
+      transaction.reset!
+      transaction.id.must_be :nil?
+      error = assert_raises Gcloud::Datastore::TransactionError do
+        transaction.rollback
+      end
+      error.wont_be :nil?
+      error.message.must_equal "Cannot rollback when not in a transaction."
+    end
+  end
 end