UL operates five testing laboratories in the United States. In the beginning, UL provided insurance companies with technical analyses in diverse fields allowing them to use the results in drawing up underwriting policies, evaluating risk, or lowering premium rates by encouraging manufacturers to improve their product quality.

UL was originally organized under the sponsorship of insurance companies. Its standards gradually became a compulsory means for satisfying consumer products safety laws that were adopted in New York, Los Angeles, Chicago, San Francisco, and some other cities in the United States. But in a strict sense, UL standards are optional, not compulsory. They must receive approval from the US Federal Government. The reliability of UL standards in the United States is highly appreciated and consumers have a high preference for products marked with UL certification. For these reasons, most manufacturers, retailers, and importers require UL certification, and it has therefore become compulsory in effect for exports to the US market.