Cultured or synthetic diamonds are diamonds which are grown in a laboratory over the course of several days, rather than formed under the Earth in a process which takes millions of years. Although some consumers dismiss synthetic diamonds as fake, they are in fact chemically identical to conventional diamonds. Because a laboratory environment allows for great control, synthetic diamonds have the potential to be of a much higher quality than those mined from the earth. Synthetic diamonds are less likely to have inclusions, and many fancy diamonds are synthetic, because the process allows for the easy introduction of impurities which will create a rich color.

The first synthetic diamond was created in 1893 by Henri Moissan, using a high pressure, high temperature process. By heating and compressing carbon, he successfully created an artificial diamond, although it was rather small. This industrial process for creating diamonds is widely used in many laboratories around the world, although gem quality synthetic diamonds tend to be made using a chemical vapor deposition process. These diamonds are grown in a low pressure environment with the use of a substrate for the diamond to grow on.

Industrial manufacturing has taken advantage of the stable quality of synthetic diamonds for several decades. Like conventional diamonds, they are extraordinarily strong, and can be used to cut through a wide variety of materials, or integrated into drills and grinders. The electronics industry is also interested in the potential uses for diamonds as semiconductors. Most large manufacturers of synthetic diamonds are focused on supplying the need for industrial diamonds, rather than gems.

Gem quality synthetic diamonds are also growing in popularity. For consumers concerned about blood or conflict diamonds, synthetic diamonds are an excellent alternative choice to conventional diamonds. In addition, synthetic diamonds tend to be cheaper, and offer a wider range of color options, carat sizes, and cuts. Currently, synthetic diamonds are usually clearly identified at the time of sale, and some diamond grading companies will not grade synthetic diamonds, although they will provide basic data about them such as their cut, carat size, and color.

Synthetic diamonds should not be confused with fake diamonds, such as cubic zirconium. Fake diamonds are made from substances which resemble diamond, but do not have the same mineral properties, structure, and chemical formula. Although false diamonds can be perfectly appropriate for some jewelry, they are not used in industrial processes because they lack the strength of true diamonds. While it may be difficult to tell the difference between a synthetic diamond and a natural one, it is very easy to identify false diamonds under a jeweler's loupe.