Those wishing to stay longer should apply in advance for a 60 day tourist visa at a local embassy - issued usually within an hour for a small fee. Alternatively you can get a 10 day extension while in Thailand for 1,900 baht at any local immigration office. Another trick is to leave at a conveniently placed border and re-enter immediately for a further 30 days.
Passports should be valid for at least six months at the time of entering Thailand. There are other classes of visa, such as the Non-immigrant visa, which allows people the right to remain for three months and extend if further if they have a good excuse - such as taking up employment, studying, undertaking voluntary work and so on, but documentation needs to be provided when applying outside of the country.
