Generally, a visa is required in Thailand, however, other national countries are not required to apply for a tourist visa when visiting the country. In compliance with the new visa exemption list presented below, the following countries are eligible to enter Thailand without a visa through the land-border checkpoint for only twice a year. Entering the country through international airports will not be affected by this regulation.

Nationals of the following countries and territories are entitled to a 30-days visa exemption:

Nationals from other countries and territories are required to obtain a visa in accordance with their purpose of visit. Delegates are advised to obtain a tourist visa. A tourist visa is a 60-day visit in the country. This can be extended up to another 30-days by means of a visa run. If you are planning to extend your visa, you can convert the visa to a non-immigrant visa which will require you to go to any nearby city or country such as Penang or Kuala Lumpur, Malaysia.

To learn more about obtaining a Thai visa, you can refer to the Thai Embassy's official guidelines with the link below:
http://www.thaiembassy.com/visa/thaivisa.php