A "Certified Diamond" is a Diamond which has been evaluated for it's unique properties and endorsed with a guarantee of stated quality from an independent Gemological Laboratory. A Diamond Certificate does Not establish a diamonds value, it simply helps in preventing fraud by allowing a consumer to have confidence in a purchase. Any Diamond can be "certified", regardless of size, quality or value.
There are many Diamond certification companies, each with a slightly different rating system. Below is a list of the most popular certification laboratories in order of consistency and reliability: Excellent, Very Good, Good, Fair & Poor.