Most people know the four "Cs" of diamonds that determine the value of a stone. These are cut, clarity, color and carat weight. But there's a fifth "C" you should not overlook, which is the diamond certificate. The diamond certificate---sometimes called a grading report---is a complete evaluation of your diamond that has been performed by a qualified professional with the help of special gemological instruments. Each stone bears its own recognizable, individual characteristics, which are listed on the certificate. Be wary of investing in a diamond without one.