When people talk about the cut of a diamond, they are referring to how it is shaped and polished, the way its sides, or facets, are designed, and how shallowly or deeply it has been cut. Diamond cutting styles are innumerable, but there are a great many that have been patented and among superficially similar patented types, there are many differences. Princess and Asscher diamond cuts, for instance, are both square shaped. But the facets of each are cut and arranged in extremely different ways.

People might also mean the shape of a diamond when they speak of its cut. A diamond's shape is predetermined in large part by its molecular structure. Diamonds whose molecular crystals are macers, can be cut to be oval or marquise shaped, while those that have an octahedron structure must be cut to be a round brilliant. Certain crystal structures permit several cutting options. Octahedron diamonds can often be turned into two round brilliants.

Most diamond cuts do not have sharp corners, but corners that are cut off and rounded. This is because, counter to the popular myth, diamonds can be quite brittle and do chip when they bump into things at the wrong angle. So leave the glass cutting to specialized bits! Because of this, the Princess cut is unique among diamonds with its squared shape and fully pointed corners. An emerald shaped diamond may be rectangular, but its corners are rounded. Its sides, or facets, are also longer than a Princess cut diamond. Emerald cuts are used for diamonds that have a high level or clarity, that are not cloudy at all, because it accentuates the transparency of the stone. If the diamond is not clear, it will seem clouded, which is unappealing.

Modern round cut brilliant stones are not actually round, but have 58 or 57 facets. Those that have 58 facets maintain the small, bottom facet called the culet. Those that have only 57 have omitted the culet. The Marquise cut is interesting in that it is a cut that can maximize the weight of a stone in carats, because although it can be a long and slim cut, it is highly faceted. Marquise cut diamonds can be shaped in many different length-width ratios. The Asscher diamond cut is related to the emerald cut, save that instead of being rectangular, it is square. When it is viewed top-down, the cut looks a lot like a spider web does.

Other cuts are mostly what their name implies. Tear and pear cut diamonds are diamonds that are cut to resemble tears or pears. They are ovals that are thinner on one side than on the other, with rounded curves. Oval cut diamonds are simply an oval. Heart shaped diamonds are heart shaped.