GIA stands for the Gemological Institution of America; they are a highly respected certification group throughout the world. Although GIA is common throughout Europe and Asia, here in America, it is the IGI or International Gemological Institute that is more common. However, when you are shopping for a diamond, you should give preference to those diamonds that are GIA certified.  GIA has a strict and consistent grading system From the beginning, GIA's mission was to create a methodology that could be applied to diamonds that would lead to a consistent assessment of each diamond.