GIA stands for Gemological Institute of America. They are well-known throughout the industry and have a global presence with two laboratories in the US, one in California and one in New York.
Out of all of the grading laboratories, the GIA is the most accurate, most trusted, and most well-known lab in the industry. We prefer and sell GIA diamonds for that very reason. What we have found is that other labs like AGS, IGI, and some EGLs tend to grade loosely which means you could pay for what appears to be a high quality diamond, but in reality isn't as good a quality and therefore should be priced less.