When you buy a diamond, you want to be sure it's been examined by a reputable gemological expert so that you can be guaranteed that you're getting what you're paying for. Diamonds are judged on the 4 Cs - clarity, cut, color and carat. When a diamond is graded, it helps determine its value, so it makes sense to have any diamond you're considering buying examined by someone from one of the institutes that do so. Keep reading to find out which ones are the best.