Steam is a video game digital distribution platform developed by Valve Corporation. It was launched in September 2003 as a way for Valve to provide automatic updates for their games, but eventually expanded to include games from third-party publishers. Steam offers digital rights management (DRM), matchmaking servers, video streaming, and social networking services. It also provides the user with installation and automatic updating of games, and community features such as friends lists and groups, cloud saving, and in-game voice and chat functionality.

The software provides a freely available application programming interface (API) called Steamworks, which developers can use to integrate many of Steam's functions into their products, including matchmaking, in-game achievements, microtransactions, and support for user-created content through Steam Workshop. Though initially developed for use on Microsoft Windows operating systems, versions for macOS and Linux were later released. Mobile apps were later released for iOS, Android, and Windows Phone in the 2010s. The platform also offers a small selection of other content, such as design software, game soundtracks, anime, and films.

The Steam platform is the largest digital distribution platform for PC gaming, estimated in 2013 to have 75% of the market space.[4] By 2017, users purchasing games through Steam totaled roughly US$4.3 billion, representing at least 18% of global PC game sales.[5] By 2019, the service had over a billion registered accounts with 90 million monthly active users. The success of the Steam platform has led to the development of a line of Steam Machine microconsoles, which include the SteamOS operating system and Steam Controllers, and the Steam VR platform.