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 are nationals of countries which are exempted from visa requirements when entering Thailand for tourism purposes. For more information, please see
Summary of Countries and Territories entitled for Visa Exemption and Visa on Arrival to Thailand.
For further information please visit:
http://www.mfa.go.th/main/en/services/4908/15405-General-information.html