A diamond solitaire is a diamond which is set alone, in a distinctive setting which showcases the stone. Classically, a diamond solitaire is large, and the stone may appear totally alone, or it may be surrounded with accent stones. Other types of gemstones may also be displayed in a solitaire setting, or used as accent stones with a diamond solitaire.

The practice of setting remarkable stones on their own to attract attention and capture the eye is ancient. In a diamond solitaire, the setting is often designed to be as unobtrusive as possible, so that the stone can clearly be seen. A wide variety of cuts may be used, depending on the diamond's natural properties, and both plain and fancy diamonds may be displayed in a solitaire setting. In either case, the diamond must be as flawless as possible, with few to no inclusions and a clear, bright appearance, because the solitaire setting leaves little room for error.

In a classic diamond solitaire setting, the stone is displayed on its own in a prong setting. In the case of rings, the band size is carefully calibrated to ensure that it complements and supports the stone without overwhelming it. Diamond solitaires can also be used in bracelets, necklaces, earrings, and brooches. The single stone must be large to be clearly visible, which can make solitaire settings expensive, as carat size is a major factor in cost.

In other versions of the diamond solitaire, a single stone is surrounded by accent stones which are considerably smaller. Depending on the taste of the designer, the solitaire stone may be especially large so that it stands out, or it may be more modestly sized, for a streamlined look which is designed to be more graceful. The accent stones may be diamonds, but they can also be other precious stones, such as sapphires, rubies, or emeralds.

When selecting a diamond solitaire, the buyer should assess the appearance of the stone carefully. Whether the diamond is “fancy,” an industry trade term for “colored,” or not, it should be cut in a way which brings out the natural sparkle and shine of the diamond. It should also be highly clear, and it should be firmly seated in the setting, with no signs of wobbling or weakness. It is also important to maintain diamond solitaire jewelry well, to ensure that dirt and grime do not adhere to the stone, obscuring its sparkle.