Lichess is a free and open-source Internet chess server run by a non-profit organization of the same name. Users of the site can play online chess anonymously and optionally register an account to play rated games. Lichess is ad-free and all the features are available for free, as the site is funded by donations from patrons. Features include chess puzzles, computer analysis, tournaments and chess variants.

Online chess is chess that is played over the Internet, allowing players to play against each other in real time. This is done through the use of Internet chess servers, which often include a system to pair up individual players based on their rating using an Elo or similar chess rating system. Online chess has existed since the 1970s, but has seen a rapid growth in popularity amidst the COVID-19 pandemic and rise of chess livestreaming.