合成钻石或称人造钻石，即透过技术加工制成的钻石，对比于地质作用自然形成的天然钻石。合成钻石也广泛被称作HPHT钻石和CVD钻石，分别表示它的加工方式：高温高压（High-Pressure High-Temperature）以及化学气相沉积（Chemical Vapor Deposition）。

1879年至1928年间，许多学者提出了钻石合成的假设；它们虽然经过仔细的分析、推论，但始终没有付诸实行。1940年代，美国、瑞典和苏联率先投入钻石合成研究，因而发现了CVD及HPHT合成技术。第一个可复制合成技术于约1953年见世。此后CVD和HPHT钻石一直支配着合成钻石市场，直到1990年代晚期出现了第三种合成技术：爆压法，即直接以炸药本身所含之碳元素，经过爆炸，合成奈米尺寸钻石颗粒。第四种合成技术、即将石墨经由高能超声波处理，也随后在实验室中被证实，但现今尚未应用在商业领域。 2010年蒙宇飞博士合成出目前世界上最大的无色切割CVD钻石，重达2.3克拉。

A synthetic diamond (also known as an artificial 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). While the term synthetic is associated by consumers with imitation products, artificial diamonds are made of the same material (pure carbon, crystallized in isotropic 3D form). 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".