Here is what I have for you, straight from their web site.
Underwriters Laboratories Inc. (UL) is an independent, not-for-profit product safety testing and certification organization. We have tested products for public safety for more than a century. Each year, more than 17 billion UL Marks are applied to products worldwide.
Since our founding in 1894, we have held the undisputed reputation as the leader in U.S. product safety and certification. Building on our household name in the United States, UL is becoming one of the most recognized, reputable conformity assessment providers in the world. Today, our services extend to helping companies achieve global acceptance for their products, whether it is an electrical device, a programmable system or a company's quality process.