The round brilliant shape is currently the most popular of diamond shapes, with some figures showing it to account for over 75% of all diamond transactions. It is just one of many shapes within the diamond world, but it has been set apart from other diamond shapes. The primary reason for this is that the round brilliant shape is capable of maximizing the display of light within the diamond. Due to the popularity of this diamond shape, in addition to the available measurements for the round brilliant, gemological laboratories are set up to measure and report on the characteristics of this shape more than any of the Fancy shapes. It is within the round brilliant shape that the ideal cut diamond is found.

The greater expense of the modern round brilliant is not due only to its sustained popularity. There are two other primary reasons for the greater expense that is found in round brilliants, as opposed to other diamond shapes. The first is related directly to the greater amount of rough diamond that is lost when the round is being cut and polished. As a diamond's carat weight is one of the main determinants of the diamond's value, a shape that is costly to carat weight is going to demand a higher expense. The second is due to the longer cutting and polishing time required for round brilliants. The more labor the cutter has to put into a diamond, the more money the cutter will need in order to make it worth her or his time.

The 58 faceted round brilliant diamond has not been with us since the beginning of the use of diamonds as gemstones. The round brilliant shape finds its origins in the single cut type of diamond, which had a broad table with 8 facets on the crown, and 8 facets on the pavilion. By the 17^th century, this cut developed into the double cut, also known as the Mazarin cut, which had 16 facets on the crown (17 including the table), 16 on the pavilion, and had developed a culet. Within the same century, Vincent Peruzzi took the double cut and reshaped it into the triple cut. This became known as the Peruzzi cut and, complete with 58 facets, was the direct precursor of the first modern brilliant round.

The modern proportions for the brilliant cut were first developed by Henry Morse in the 19^th century. It due to his studies with the brilliant cut that Marcel Tolkowsky was able to formulate the mathematical models for the ideal cut round brilliant shape. In the first quarter of the 20^th century Tolkowsky utilized the available information on the brilliant cut and theorized that the round shape would be best suited to maximize the brilliance and fire displays of light in diamonds. The round shape had been in use up to this time, as is evidenced in the Old European cut, which both Morse and Tolkowsky had used in creating their respective models for the brilliant cut. However, with Tolkowsky's research and mathematical modeling, the modern brilliant round diamond came to the forefront of diamond shapes.

Ideal cut round brilliants are far more labor intensive than other round brilliants and this is due to the greater exactitude required of the diamond cutter during all phases of the diamond shaping. The table percentage, the pavilion percentage, and each and every facet must be cut and polished to a degree of perfection that has been laid out according to mathematical formulation for the greatest effect of brilliance and fire. The ideal cut round brilliant is also more costly to the overall carat weight of the rough diamond than other round brilliants. This is why ideal cut round brilliants tend to be the most costly of all diamond shapes, all other aspects being equal.