Diamonds come in a variety of shapes, sizes, colour and cut. Round brilliant cut, princess cut, emerald, asscher, marquise, oval, pear, heart, cushion, radiant and trilliant cut are the main diamond shape and cutting styles. The most popular and traditional shape for a solitaire diamond engagement ring is a round brilliant cut diamond. Princess, Asscher and Cushion cut diamonds are excellent choices for diamond engagement ring designs that require a square centre stone. Radiant and Emerald cut diamonds are both rectangular in shape. Oval, Pear, Marquise, Trilliant and Heart shape diamonds lend themselves to unique ring designs and are often complemented by smaller diamonds on each side which are known as shoulder stones.