Ordinary passport holders from many Western and Asian countries, including most ASEAN countries, Australia, Canada, most European Union countries, Hong Kong, Japan and the United States do not need a visa if their visit is for tourism. Visitors arriving by air are granted a 30-day permit (with the exception of nationals from Korea, Brazil, Chile and Peru, who receive 90 days), but since 15 December 2008, visitors arriving by land are only entitled to 15 days (visitors from several countries, mainly neighbouring countries but especially Russia, continue to receive 30 days due to the bilateral visa waiver at the land border). The Thai Immigration Department requires that visitors’ passports have a minimum validity of 6 months and that there is at least one completely blank visa page. For passport holders from 28 other nations (Bhutan, China, Estonia, India, Kazakhstan, Latvia, Liechtenstein, Lithuania, Maldives, Mauritius, Oman, Poland, Russia, Saudi Arabia, Slovakia, Slovenia, Uzbekistan, Ukraine, Ethiopia, Taiwan, Bulgaria, Andorra, Malta, Romania, San Marino, Czech Republic, Hungary, Cyprus), a visa on arrival is possible at some entry points. Consult the latest information from the Ministry of Foreign Affairs. Law you must carry your passport with you at all times.
Those who have passports from little-known countries, including European city states, or who have problems with document forgery, must obtain a visa in advance from the nearest Thai embassy. This applies even if the visa is technically allowed on arrival. There are reports of tourists being detained with valid passports, which are not common in Thailand. Also, ask for a business card of the person or embassy that issued the visa so that they can be contacted on arrival if necessary. Those without an embassy in Bangkok should enquire about the third country that represents their interests in the city, as well as the local means of contact.
It is well known that proof of subsequent transit, long ignored by Thai immigration, is sometimes strictly enforced (the airlines, which have to pay for your return flight if immigration does not let you in, also check this). Printing out an electronic ticket on a budget airline is enough to convince law enforcement, but those who want to continue their journey by land may have to be a little creative. It is also possible to buy a fully refundable ticket and have it refunded in Thailand. Land crossings, on the other hand, are very simple and no proof of onward travel is required (unless the border authorities decide otherwise).
Exceeding the length of stay in Thailand is questionable. If you go to immigration and overstay by less than 10 days, you will probably be allowed to leave with a fine of 500 baht per day. However, if the police catch you overstaying for any reason, you will be taken by car to the notoriously nasty place where the illegal immigrant cages are located and you may be blacklisted in Thailand. For most people, it’s not worth the risk: get a legal extension or make a visa run at the next border instead.
Thai immigration officials at land border crossings have been known to demand a bribe of about 20 baht per person from foreigners before stamping your passport. Immigration officials at airports do not usually ask for bribes.