diff --git a/lib/heap/client.rb b/lib/heap/client.rb
index e1d16ba..4c03775 100644
--- a/lib/heap/client.rb
+++ b/lib/heap/client.rb
@@ -106,7 +106,8 @@ def add_user_properties(identity, properties)
   #   each value must be a Number or String with fewer than 1024 characters
   # @return [HeapAPI::Client] self
   # @see https://heapanalytics.com/docs/server-side#track
-  def track(event, identity, properties = nil)
+  def track(event, identity, properties = nil, options = {})
+    options ||= {}
     ensure_valid_app_id!
 
     event_name = event.to_s
@@ -123,6 +124,14 @@ def track(event, identity, properties = nil)
       ensure_valid_properties! properties
     end
 
+    unless options[:timestamp].nil?
+      body[:timestamp] = ensure_valid_timestamp!(options[:timestamp])
+    end
+
+    unless options[:idempotency_key].nil?
+      body[:idempotency_key] = ensure_valid_idempotency_key!(options[:idempotency_key])
+    end
+
     response = connection.post '/api/track', body,
         'User-Agent' => user_agent
     raise HeapAPI::ApiError.new(response) unless response.success?
diff --git a/lib/heap/validations.rb b/lib/heap/validations.rb
index e409641..0c6d7a9 100644
--- a/lib/heap/validations.rb
+++ b/lib/heap/validations.rb
@@ -1,4 +1,5 @@
 # Internal methods used to validate API input.
+require 'date'
 
 class HeapAPI::Client
   # Makes sure that the client's app_id property is set.
@@ -43,6 +44,45 @@ def ensure_valid_identity!(identity)
   end
   private :ensure_valid_identity!
 
+  # Validates timestamp, making sure it's a valid iso8061 timestamp or
+  # number of milliseconds since epoch
+  #
+  # @param [String|Integer|DateTime|Time] timestamp
+  # @raise ArgumentError if timestamp is of an invalid type
+  # @return [String] unix epoch milliseconds or iso8061
+  def ensure_valid_timestamp!(timestamp)
+    if timestamp.kind_of?(Time)
+      timestamp = timestamp.to_datetime
+    end
+    if timestamp.kind_of?(DateTime)
+      timestamp = timestamp.strftime('%Q').to_i
+    end
+    if timestamp.kind_of?(String) && iso8601?(timestamp)
+      timestamp
+    elsif timestamp.kind_of?(Integer)
+      timestamp.to_s
+    else
+      raise ArgumentError,
+        "Unsupported timestamp format #{timestamp}. " +
+        "Must be iso8601 or unix epoch milliseconds."
+    end
+  end
+  private :ensure_valid_timestamp!
+
+  # Validate idempotency_key, making sure it's a string
+  #
+  # @param [String|Integer] idempotency_key
+  # @raise ArgumentError if identity is of an invalid type or too long.
+  # @return [String] stringified idempotency_key
+  def ensure_valid_idempotency_key!(idempotency_key)
+    unless idempotency_key.kind_of?(String) || idempotency_key.kind_of?(Integer)
+      raise ArgumentError, "Unsupported idempotency key format for " +
+        "#{idempotency_key}. Must be string or integer"
+    end
+    idempotency_key.to_s
+  end
+  private :ensure_valid_idempotency_key!
+
   # Validates a bag of properties sent to a Heap server-side API.
   #
   # @param [Hash<String, String|Number>] properties key-value property bag;
@@ -74,4 +114,12 @@ def ensure_valid_properties!(properties)
     end
   end
   private :ensure_valid_properties!
+
+  def iso8601?(string)
+    Time.iso8601(string)
+    true
+  rescue ArgumentError
+    false
+  end
+  private :iso8601?
 end
diff --git a/test/client_track_test.rb b/test/client_track_test.rb
index 79a6aae..cae4f5f 100644
--- a/test/client_track_test.rb
+++ b/test/client_track_test.rb
@@ -121,6 +121,33 @@ def test_track_with_array_property_value
         exception.message
   end
 
+  def test_track_with_non_date_timestamp
+    exception = assert_raises ArgumentError do
+      @heap.track 'test_track_with_array_property_value', 'test-identity', {}, :timestamp => 'foobar'
+    end
+    assert_equal ArgumentError, exception.class
+    assert_equal 'Unsupported timestamp format foobar. Must be iso8601 or unix epoch milliseconds.',
+        exception.message
+  end
+
+  def test_track_with_array_timestamp
+    exception = assert_raises ArgumentError do
+      @heap.track 'test_track_with_array_property_value', 'test-identity', {}, :timestamp => []
+    end
+    assert_equal ArgumentError, exception.class
+    assert_equal 'Unsupported timestamp format []. Must be iso8601 or unix epoch milliseconds.',
+        exception.message
+  end
+
+  def test_track_with_array_idempotency_key
+    exception = assert_raises ArgumentError do
+      @heap.track 'test_track_with_array_property_value', 'test-identity', {}, :idempotency_key => []
+    end
+    assert_equal ArgumentError, exception.class
+    assert_equal 'Unsupported idempotency key format for []. Must be string or integer',
+        exception.message
+  end
+
   def test_track
     @stubs.post '/api/track' do |env|
       golden_body = {
@@ -174,6 +201,67 @@ def test_track_with_properties
         'test-identity','foo' => 'bar', :heap => :hurray)
   end
 
+  def test_track_with_timestamp
+    @stubs.post '/api/track' do |env|
+      golden_body = {
+        'app_id' => 'test-app-id',
+        'identity' => 'test-identity',
+        'event' => 'test_track_with_timestamp',
+        'properties' => {},
+        'timestamp' => '1524038400000'
+      }
+      assert_equal 'application/json', env[:request_headers]['Content-Type']
+      assert_equal @heap.user_agent, env[:request_headers]['User-Agent']
+      assert_equal golden_body, JSON.parse(env[:body])
+
+      [200, { 'Content-Type' => 'text/plain; encoding=utf8' }, '']
+    end
+
+    assert_equal @heap, @heap.track('test_track_with_timestamp',
+      'test-identity', {}, :timestamp => Time.parse("2018-04-18 08:00:00 UTC"))
+  end
+
+  def test_track_with_iso8601_timestamp
+    timestamp = "2018-04-18T22:42:38+03:00"
+    @stubs.post '/api/track' do |env|
+      golden_body = {
+        'app_id' => 'test-app-id',
+        'identity' => 'test-identity',
+        'event' => 'test_track_with_iso8601_timestamp',
+        'properties' => {},
+        'timestamp' => timestamp
+      }
+      assert_equal 'application/json', env[:request_headers]['Content-Type']
+      assert_equal @heap.user_agent, env[:request_headers]['User-Agent']
+      assert_equal golden_body, JSON.parse(env[:body])
+
+      [200, { 'Content-Type' => 'text/plain; encoding=utf8' }, '']
+    end
+
+    assert_equal @heap, @heap.track('test_track_with_iso8601_timestamp',
+      'test-identity', {}, :timestamp => timestamp)
+  end
+
+  def test_track_with_idempotency_key
+    @stubs.post '/api/track' do |env|
+      golden_body = {
+        'app_id' => 'test-app-id',
+        'identity' => 'test-identity',
+        'event' => 'test_track_with_idempotency_key',
+        'properties' => {},
+        'idempotency_key' => 'foobar35214532512'
+      }
+      assert_equal 'application/json', env[:request_headers]['Content-Type']
+      assert_equal @heap.user_agent, env[:request_headers]['User-Agent']
+      assert_equal golden_body, JSON.parse(env[:body])
+
+      [200, { 'Content-Type' => 'text/plain; encoding=utf8' }, '']
+    end
+
+    assert_equal @heap, @heap.track('test_track_with_idempotency_key',
+      'test-identity', {}, :idempotency_key => 'foobar35214532512')
+  end
+
   def test_track_error
     @stubs.post '/api/track' do |env|
       [400, { 'Content-Type' => 'text/plain; encoding=utf8' }, 'Bad request']