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.