Diamond grading reports or certificates from reputable gemological laboratories date back to the middle of the 20^th century and they have become an enormous important part of the modern diamond trade. 

Gemological laboratories grade hundreds of thousands of diamonds a year that much repetition makes grading on the reports highly reliable and consistent, another factor that contributes to the accuracy of the grades is that, at most labs, several graders examine each diamond.

Diamond certificates, are becoming more and more common especially with stones over 1.00 carat or of a certain colour. 

A customer feels more safe and confident when the diamond is about to purchase comes with a certificate or report from a reliable gem Lab. The stones also costs more both because of the value the Laboratory holds and because it costs money for the certification itself.

In Europe 2 reputable diamond labs are HRD and IGI.

World Wide the most trusted lab is GIA. This is because they are the most consistent, they r ahead of any other lab in research, and after all they came up with the grading systems we all use today!