One of the first things most people learn about diamonds is that not all diamonds are created equal. In fact, every diamond is unique. Diamonds come in many sizes, shapes, colors, and with various internal characteristics. All polished diamonds are valuable. That value is based on a combination of factors. Rarity is one of those factors. Diamonds with certain qualities are more rare—and more valuable—than diamonds that lack them. Jewelry professionals use a systematic way to evaluate and discuss these factors. Otherwise, there would be no way to compare one diamond to another. And there would be no way to evaluate and discuss the qualities of an individual diamond. Diamond professionals use the grading system developed by GIA in the 1950s, which established the use of four important factors to describe and classify diamonds: Clarity, Color, Cut, and Carat Weight.