.th is the Internet country code top-level domain (ccTLD) for Thailand. It was developed through experiments during the inauguration of internet connection in Thailand in 1986 by Dr. Kanchana Kanchanasut and Dr. Tonomori Kimura, professors of the Asian Institute of Technology (AIT), at they worked to connect to university computer networks to send and receive email with colleagues at the University of Melbourne Australia and University of Tokyo Japan. As the software required a domain name, a country code had to be incorporated into the domain name system using .th.

.th domain name registration is divided into seven categories, ac.th, co.th, go.th, mi.th, net.th, or.th and .in.th. Domain name registrants must be verified before receiving approval. The registration of domain names must be conducted in good faith and have a contact person with a residential or office address in Thailand.