There are nearly 50 Countries and Territories entitled for Visa Exemption to Thailand. Nearly 20 nationals could apply for Visa on Arrival. There are 10 types of Visa in total:

Transit Visa (TS)-- To transit to third country
Tourist Visa (TR) -- Tourism
Non-Immigrant (B) -- To conduct business activities
Non-Immigrant (ED) -- To attend seminar or training courses in Thailand / To study in Thailand
Non-Immigrant (F) -- To attend official meeting or official business in Thailand
Non-Immigrant (O) -- Other purposes such as visiting or accompanying relatives in Thailand
Non-Immigrant (OA) -- Only for the person who 50 years of age and above. (Employment in Thailand is prohibited)
Diplomatic -- Only for diplomatic or official passport holders who will assume duties in Diplomatic Mission or International Organization in Thailand or who will enter Thailand on official duty
Official -- For those who will enter Thailand on official duty or as guest of the Thai government or other purposes
Courtesy -- For those who will enter Thailand on official duty or as guest of the Thai government or other purposes

Visa Exemption and Visa on Arrival to Thailand
Visa requirement to Thailand

Visa on Arrival
According to the Interior Ministerial Announcements, passport holders from 20 countries may apply for visas at the immigration checkpoints for the purpose of tourism for the period of not exceeding 15 days. Please prepare documents as below:

1. Passport with validity of more than 6 months together with an application form and a passport size photograph (2 inches)
2. Cash 10,000 (person) or 20,000 (family) Thai Baht or equivalent amount that will be randomly checked by the Immigration officers
3. Round trip air ticket not exceeding 15 days

Visitors who enter the Kingdom with Visa on Arrival generally cannot file an application for extension of stay except in special cases such as illness which prevents them from traveling, etc. They can submit an application at the Office of Immigration Bureau , Immigration Division 1, 57 Soi Suan Plu, South Sathorn Road, Bangkok 10120.
Tel: (662) 287-3127 or 287-3101-10 ext. 2264-5
http://www.immigration.go.th/nov2004/en/base.php

For more information please see The Consular Section of the Royal Thai Embassy in China: http://www.thaiembbeij.org

List of countries which are declared as Yellow Fever Infected Areas
The Ministry of Public Health has issued regulations that applicants who have travelled from or through the countries which have been declared Yellow Fever Infected Areas must provide an International Health Certificate proving that they have received a Yellow Fever Vaccination

The International Health Certificate must be submitted together with the visa application form. The traveler will also have to present the said certificate to the Immigration Officer upon arrival at the port on entry into Thailand. As for those nationals of the countries on the list but who have not travelled from/through those countries, such a certificate is not required. However, they should possess concrete evidence showing that their domicile is not in an infected area so as to prevent unnecessary inconvenience. (please click here for list of countries)

Nationalities which require special visa application channel
National of certain countries requires special channel of visa application; some are required to apply for visa only at the Royal Thai Embassy or Royal Thai Consulate-General in their home/residence country or at the designated Thai Embassy. Therefore, travelers are advised to contact the nearest Thai Embassy or Consulate-General to find out where and how they may apply for visa to Thailand before their departure.