The round brilliant cut diamond is by far the most popular and most researched diamond shape available today. For almost 100 years, diamond cutters have been using advanced theories of light behavior and precise mathematical calculations to optimize the glitter and sparkle in a round diamond. In addition to being the most popular and researched shape, a round diamond will typically give you more flexibility in terms of balancing cut, colour, and clarity grades while still getting the glitter and sparkle you want.