You can enjoy a good 30 day stay in Thailand without a tourist visa. You are only asked for a Thai tourist visa if you wish to prolong your stay for more than a month. When you enter Thailand your passport will have the ‘VOA’ which is visa on arrival. This VOA is free and valid for about a month if you have landed by air routes. Your free visit will be shortening to 15 days if your mode of entrance to Thailand is thorough land.
If you do not fit the above criteria and you wish to stay longer than allowed than the government of Thailand requires a tourist visa which will be granted to you by the Thai Consulate or Embassy functioning in your country. Getting a Thai visa is not much of a deal, all you have to do is give in your passports with the required authentic documents.
The time period of your single entry visa stay can be extended by consulting the Thai Embassy or the immigration officer. The process of Thai visa extension will require a fee of 1900 baht.
Incase of a double entry visa which allows 6 month stay, you will follow the same procedures that of a single entry visa and pay a similar fee of 1900 baht for extending your Thai tourist visa. Once your visa date goes beyond 90 days you will have to leave the country immediately by any transport mode of your choice.
Your passport should not be expired within a course of six months and in case you breech the terms of a tourist visa you will have to face strict criminal laws of Thailand. This breech also includes working in Thailand on a tourist visa.
Though attaining a Thai visa is simple but you should be very careful to abide by all the regulations they require from there tourists.