If you stay longer than 30 days uninterrupted in Thailand you will
need a visa. There are tourist visas or
non-immigrant visas for a longer stay.
The tourist visa is good for 60
days each entry. You can get more than one entry.
Each entry with the non-immigrant visa
allows you to stay 90 days. You can get
more than one entry. You can get the non-immigrant
visa with multiple entries. Than you are allowed to leave and
enter the Kingdom of Thailand as often you want within one year. But
you have to leave Thailand even with this visa every 90 days.
You can also use the regular 30 days visa.
You have to leave Thailand every 30 days but you can re-enter Thailand
immediately. On leaving Thailand you will get a departure stamp and
after re-entering you will get a new 30 days visa for Thailand. In that way you can stay in Thailand up to 90 days. After that you have to leave Thailand for at least another 90 days.