AddThis is a media web-tracking technology company based in Vienna, Virginia, United States. The company operates AddThis.com, a social bookmarking service that can be integrated into a website with the use of a web widget. Once the widget is added, visitors to the website can bookmark an item using a variety of services, such as Facebook, MySpace, Google Bookmarks, Pinterest, and Twitter. The site reaches 1.3 billion unique visitors monthly and is used by more than 14 million web publishers.