Upon arrival in Thailand, foreign citizens must hold a valid passport with at least six months validity, a valid Thai visa, and proof on onward travel. However, visitor from ASEAN or Western countries, including most European, Commonwealth, and North American citizens, are not required to have a Thai visa for visits less than 30 days in Thailand. They will be granted access through Thailand immigration with a 30 Thai visa waiver, provided upon arrival. After such time, a Thai visa extension from an immigration office or a Thailand visa from an embassy or consulate outside of Thailand is required. Immigration policies are subject to change: check with a Thai Embassy or Thai Ministry of Foreign Affairs for the latest information.

Generally, a foreign citizen who wishes to enter the Kingdom of Thailand is required to obtain a visa from a Royal Thai Embassy or a Royal Thai Consulate-General. However, nationals of certain countries do not require a visa if they meet visa exemption requirements. 

List of visa exempted Nationals:

Australia Austria Belgium Brazil
Bahrain Brunei Darussalam Canada Denmark
Finland France Germany Greece
Hong Kong Iceland Indonesia Ireland
Israel Italy Japan Korea
Kuwait Luxembourg Malaysia Monaco
Netherlands New Zealand Norway Oman
Peru Philippines Portugal Qatar
Singapore Spain South Africa Sweden
Switzerland Turkey Vietnam United Kingdom
United States of America United Arab Emirates Czech Republic Hungary
Liechtenstein Poland Slovak Republic Slovenia