Synthetic diamond (also known as laboratory-created diamond, laboratory-grown diamond, cultured diamond or cultivated diamond) is diamond produced in an artificial process, as opposed to natural diamonds, which are created by geological processes. Synthetic diamond is also widely known as HPHT diamond or CVD diamond after the two common production methods (referring to the high-pressure high-temperature and chemical vapor deposition crystal formation methods, respectively).

Although often referred to as synthetic, this term has been considered somewhat problematic. In the U.S., the Federal Trade Commission has indicated that the alternative terms laboratory-grown, laboratory-created, and [manufacturer-name]-created "would more clearly communicate the nature of the stone", as consumers associate the term synthetic with imitation products – whereas man-made diamonds are actual diamond material.

Numerous claims of diamond synthesis were documented between 1879 and 1928; most of those attempts were carefully analyzed but none were confirmed. In the 1940s, systematic research began in the United States, Sweden and the Soviet Union to grow diamonds using CVD and HPHT processes. The first reproducible synthesis was reported around 1953. Those two processes still dominate the production of synthetic diamond. A third method, known as detonation synthesis, entered the diamond market in the late 1990s. In this process, nanometer-sized diamond grains are created in a detonation of carbon-containing explosives. A fourth method, treating graphite with high-power ultrasound, has been demonstrated in the laboratory, but currently has no commercial application.