Synthetic gems are superlative examples of crystal growth. Today, industrial and scientific crystal growth is a highly sophisticated endeavor employing a wide range of methods. Many of these have been adapted to grow gems for jewelry use. Most major gemstones have been synthesized, and these products are commercially available around the world, often at a fraction of the cost of a natural gem of comparable size and quality. Distinguishing them from their natural equivalents involves a number of interesting challenges. Inclusions (internal features) observed by microscopy often provide conclusive proof of synthetic origin. When routine testing procedures (refractive index, specific gravity, fluorescence, and internal inclusions) do not provide sufficient evidence, laboratories must employ more advanced analytical instrumentation.