According to the Interior Ministerial Announcements , passport holders from 39 countries ( include european countries ) do not require a visa when entering Thailand for tourism purposes if their stay in the Kingdom does not exceed 30 days.

This visa can be extended from 7 to 30 days at the office of Immigration Office for 1900 bath.
One condition , passport or travel document with validity not less than 3 months

You can also leave the Kingdom ( even in the same day ) for having an autorization of 30 days.
Be careful : For all overstaying , a fee of 500 bath per day is request , to be payed at Overstay Office at Airport.

Consult the latest updates on the Web Site of Ministry of Foreign Affairs , Kingdom of Thailand http://www.mfa.go.th ( in english )

TOURIST VISA EXEMPTION

          -  According to the Interior Ministerial Announcements dated 6 February B.E.2538 (1995), 8 December B.E. 2541 (1998)  1 October B.E. 2545 (2002) and 20 December B.E. 2545 (2002) , passport holders from 39 countries do not require a visa when entering Thailand for tourism purposes if their stay in the Kingdom does not exceed 30 days.

          -  The applicant must possess instrument of means of living expenses 10,000 Baht per person and 20,000 Baht per family accordingly.

          -  Please also be advised that ordinary passport holders of 39 countries who intend to engage in certain activities are eligible to apply for a visa when entering the Kingdom if their qualifications meet the conditions set forth by the Office of Immigration Bureau. For more information, please contact the Office of Immigration Bureau, Soi Suan Plu, off South Sathorn Road, Bangkok 10120, Tel. (662) 287-3101-10 or at website http://police.go.th/
 
 • List of 39 countries are as follow:
  
 1. Australia   :  Commonwealth of Australia
 2. Austria  :  Republic of Austria
 3. Belgium  :  Kingdom of Belgium 
 4. Brazil  :  Federative Republic of Brazil   
 5. Bahrain  :  State of Bahrain
 6. Brunei Darussalam  :   Negara Brunei  Darussalam
 7. Canada
 8. Denmark  :  Kingdom of Denmark
 9. Finland  :  Republic of Finland
10. France  :  French Republic
11. Germany  :  Federal Republic  of Germany
12. Greece  :  Hellenic Republic
13. Hong Kong  :  Hong Kong Special Administrative Region
14. Indonesia  :  Republic of Indonesia
15. Ireland  :  Republic of Ireland
16. Israel   :  State of Israel
17. Italy   :  Republic of Italy
18. Japan
19. Korea  : Republic of Korea
20. Kuwait  :   State of Kuwait
21. Luxembourg :  Grand Duchy of Luxembourg
22. Malaysia 
23. Netherlands :  Kingdom of the Netherlands
24. New Zealand  
25. Norway  :  Kingdom of Norway
26. Peru  : Republic of Peru
27. Philippines  :  Republic of the Philippines
28. Portugal  :  Republic of Portugal
29. Qatar  :  State of Qatar
30. Singapore  :  Republic of Singapore
31. Spain   :  Kingdom of Spain
32. South Africa :  Republic of South Africa
33. Sweden  :  Kingdom of Sweden
34. Switzerland :  Swiss Confederation
35. Turkey  :   Republic of Turkey
36. United Arab Emirates
37. United Kingdom :  United Kingdom of Great Britain and Northern Ireland
38. United States of America
39. Vietnam : Socialist Republic of Vietnam