VK (originally VKontakte) is the largest European online social networking service. It is based in St. Petersburg. It is available in several languages, but is especially popular among Russian-speaking users. Like other social networks, VK allows users to message each other publicly or privately, to create groups, public pages and events, share and tag images, audio and video, and to play browser-based games.

As of June 2016, VK had at least 369 million accounts. VK is ranked 22 (as of November 1, 2014) in Alexa's global Top 500 sites and is the most visited website in Russia, before Yandex. According to eBizMBA Rank, it is the 8th most popular social networking site in the world. VK had an average of 75 million daily users for December 2012.