The cut of a diamond is the only characteristic that is within a human's control. It is the geometric proportions to which the stone was crafted by the diamond cutter. It must be cut to precise angles, cannot be too shallow or deep, and must be polished to have a mirror finish. In order to reflect light, facets are cut to give the stone a prism-like effect.

An ideal cut is a specific cut in which the light will enter the diamond to be reflected and dispersed through the top and not the sides or the bottom. It will have good symmetry and the facets will be well aligned. It will be well polished, have a girdle that is not to thin, and a crown that is not to shallow or deep. Most importantly, the diamond will be cut to show its true brilliance.

Many diamonds will come with a diamond grading report, which is created by an independent gemological laboratory. The Gemological Institute of America does not evaluate a diamond’s cut, however the American Gem Society has it’s own rating scale which ranges from 0 (ideal) and 10 (poor). It’s a good idea to find out from your jeweler if the diamond you are interested in has been graded to determine the actual cut.

	Round (Brilliant) – The most common style of cutting for diamonds and other stones. The standard round brilliant consists of a total of 58 facets. Modifications of the brilliant style of cutting include such fancy shapes as the marquise, oval, pear shape and many others.
	Princess – A square shaped, modified brilliant cut diamond. This is a relatively new and highly popular cut for diamond engagement rings. This cut is based on the multi-faceted square cut.
	Emerald – A form of "step cutting". Usually rectangular, it has rows (steps) of elongated facets on the crown and pavilion, parallel to the girdle. It also has very pronounced corner facets.
	Radiant – A rectangular or square shaped diamond with step-cut and scissor-cut on the crown, and a brilliant-cut on the pavilion. This cut has a total of 70 emerald-type facets. Some claim this is a more brilliant diamond cut than the emerald.
	Oval – A brilliant style of cutting in which the outline is elliptical or oval. This is a slightly elongated version of the Brilliant, or Round, cut.
	Pear – A variation of the brilliant cut, having a pear or teardrop shaped girdle outline that is rounded on one end with the other end coming to a point.
	Marquise – A variation of the oval cut, in which the outline of the girdle is boat or almond shaped.
	Heart – A type of fancy diamond cut, which is cut to resemble the popular Valentine's Day shape.
	Asscher – A diamond cut named for its inventor, Joseph Asscher, who in 1902 developed a square cut diamond with 74 facets. The cut's wide step facets and deep clipped corners make the gemstone resemble an octagon.
	Antique Cushion – Much like the old-mine-cut, an older form of the brilliant cut, having a girdle outline approaching a square with rounded corners.
	Rose – An early style of cutting diamonds, probably originated in India. The base (back) is usually flat and the top (front) is slightly dome-shaped and covered with a varied number of triangular facets that terminate in a point, much like a shallow sided pyramid.
	Tycoon – The Tycoon cut is a departure from the other branded rectangle shapes with a radical top design which is reminiscent of the early French cut. The secret of this brilliant stone is the nine crown facet design which creates a diamond-shaped table. It's like having a diamond within a diamond.