From the time I arrived in 1994 up to 2006, foreigners could stay in Thailand as long as they wanted. I think this went back long before I arrived.

Tourist visas were good for only 2 months and a visa-on-arrival was good for only one month, so many foreigners did the so called "visa runs" to the border once per month to just step over into Cambodia / Burma / Laos / Malaysia for a few minutes and step back into Thailand for a new 30 day visa-on-arrival stamp.

That changed in October 2006, a month after the military government took power. A new rule went into effect that TOURISTS could not be in Thailand more than 90 days out of any 180 day period. For example, if they had been in Thailand 86 days, exited and re-entered then they would get a visa for only 4 days. Many guys were refused entry after 90 days.

This affected only tourists. People on non-immigrant B (business) or O (marriage or retirement) or ED (education) could stay as long as they wanted.

After the democratically elected government came back to power in early 2008, the immigration department stopped enforcing the 90 out of 180 day rule on tourists, returning to the pre-2006 status quo. I know many people who have stayed in Thailand nearly all of 2008 with no problems entering, and each time and getting 30 days for visa on arrival, no matter how long or many times they had already been in Thailand.

People have even gotten back-to-back tourist visas, i.e., they come in on a 60 day tourist visa, extend it at immigration to 90 days, then after 90 days go to an embassy in Laos or somewhere and get another 60 day tourist visa. Some have even gotten double entry tourist visas which means only one visit to an embassy gets them 6 months with just quick one border run.

However, visa-on-arrival at land borders has been reduced to 14 days, so people relying on buses instead of airplanes must now do 2 visa runs per month.

Visa-on-arrival at airports gets you 30 days per arrival.

The Thai government is encouraging foreigners to come to Thailand, due to the drop in tourism in 2008 and the world economic slowdown. As noted in another post of mine today, the immigration department, for the first time in history, made all visas free starting January 20th.

That said, I should note that before 2006, many Thai embassies and consulates would refuse to give tourist visas to people who had been staying in Thailand as a tourist for a long time. They had to enter with a visa-on-arrival for 30 days, instead of a tourist visa for 60 days (extendable to 90 days).

It varied from one embassy/consulate to another, whether or not to give a successive tourist visa.

From what I have heard from other people, there are more consulates/embassies giving back-to-back tourist visas recently, but it still varies by consulate/embassy. Also, the policy of each consulate/embassy seems to vary over time, often quickly.

Again, this affects only tourists. People with a non-immigrant visa due to marriage, retirement (age 50 or more), business, or education can get extendable longterm visas or unlimited multiple entry 1-year visas.

A big trend in 2008 was going to a Thai school to learn the Thai language, whereby the school would get you an education (ED) visa extendable to a year at a time.

This is all covered in much more detail on this page:

www.thailandguru.com/visa-to-thailand.html

All the best,
Mark