A real-time strategy (RTS) video game is a strategic game that is distinctly not turn-based. According to Brett Sperry, the phrase real-time was used to distinguish such games within the broader genre of strategic wargames, which has a longer history both inside and outside of video gaming. Some important concepts related to real-time strategy include combat- and twitch-oriented action. Other RTS gameplay mechanics implied are resource gathering, base building and technological development, as well as abstract unit control (giving orders as opposed to controlling units directly). Generally, the player is given a top-down perspective of the battlefield, though some 3D RTS games allow total freedom of camera movement. Additionally, the in-game user interface is much like a computer desktop: the player can manipulate controls and in-game units with techniques such as clicking and dragging. Each player in an RTS may interact with the game independently of other players, so that no player has to wait for someone else to finish a turn. This lends the genre well to multiplayer gaming, especially in online play, compared to turn-based games.

City-building games, construction and management simulations, and games of the real-time tactics variety are generally not considered to be “real-time strategy”, though their gameplay involves some overlapping concepts.

Precursors and early genesis

The genre that is recognized today as "real-time strategy" emerged as a result of an extended period of evolution and refinement. Games that are today sometimes perceived as ancestors of the real-time strategy genre were never marketed or designed as such at the original date of publication. As a result, designating "early real-time strategy" titles is problematic because such games are being held up to modern standards. The genre initially evolved separately in the UK and North America, afterward gradually merging into a unified worldwide tradition.

In the UK, the genre's beginning can be traced to Stonkers by John Gibson, published in 1983 by Imagine Software for the ZX Spectrum, and Nether Earth published on ZX Spectrum in 1987. In North America, the first game retrospectively classified as real-time strategy by many sources is The Ancient Art of War (1984), designed by Evryware's Dave and Barry Murry, followed by the sequel The Ancient Art of War at Sea in 1987, though Dani Bunten Berry's (of M.U.L.E fame) Cytron Masters (1982), developed by Ozark Softscape and released by SSI, also has been considered the earliest game of the genre.

Some writers list Intellivision's Utopia by Don Daglow (1982) as the first real-time strategy game. In Utopia two players build resources and carry out combat by proxy. It contains the direct-manipulation tactical combat now common in that the players can assume direct control over a PT boat and sink the opponents fishing boats. Another early example from the same year is Legionnaire on the Atari 8-bit family, written by Chris Crawford for Avalon Hill. This was effectively the opposite of Utopia, in that it offered a complete real-time tactical combat system with variable terrain and mutual-help concepts, but lacked any resource collection and economy/production concepts. As a result, this game might be better considered an early forerunner of the RTT (real-time tactics) genre.