US Commerical Services
The USCS has an excellent FAQ that discusses work visas, permits, tax regulations, and general legal requirements: http://www.buyusa.gov/thailand/en/faq.html

Also, if you are American, make sure that you read carefully through the Treaty of Amity and Economic Relations between United States and Kingdom of Thailand. Americans have unique benefits in doing business in Thailand that are not available to other nationalities. There are two primary benefits:

� The Treaty allows American companies to maintain a majority shareholding or to wholly own its company, branch office or representative office located in Thailand,

� American companies receive national treatment. That is, they may engage in business on the same basis as Thai companies, and are exempt from most of the restrictions on foreign investment imposed by the Alien Business Law of 1972.

However, there are restrictions in certain areas, such as:
1. Owning land;
2. Engaging in the business of inland communication;
3. Engaging in inland transportation and communication industries;
4. Engaging in fiduciary functions;
5. Engaging in banking involving depository functions;
6. Engaging in domestic trade in indigenous agricultural products;
7. Exploiting land or other natural resources

Read more details at the US Commercial Services website at:
http://www.buyusa.gov/thailand/en/treatyofamity.html

American Chamber of Commerce
The American Chamber of Commerce in Thailand (AMCHAM) was founded in 1956 and is an institution formed to promote trade, industry, agriculture, finance and other economic activities without seeking profit or income for distribution.

There are special requirements for membership:
http://www.amchamthailand.com/acct/asp/MembFee.asp?SponsorID=188

British Business Association (Phuket)
The BBA-P is a grouping of business people and other expatriates in Phuket whose primary goals are to exchange business information, network, promote Anglo-Thai relations, to support selected charities and to support the promotion of tourism and other beneficial developments in Phuket.

The Association was formed in the middle of 1998 and offers members and their guests a wide range of activities and benefits which include:

- Monthly social meetings
- Regular Dinner evenings with speakers
- Sponsored charity events
- Sporting Events and Activities
- Opportunities to exchange business information
- Discounts for members at selected establishments in Phuket
- Associate membership of the British Chamber of Commerce, Bangkok

Membership
Membership currently stands at over 70 members. Membership is open to all nationalities, and currently includes US, Australian, Canadian as well as British. It is just as popular with part-time residents and retirees as it is with those in employment or business. For more information contact the Hon Sec

US-ASIAN Business Council
If you don't mind the intense legal language, this site is a treasure trove of information on the requirements for doing business in Thailand. Truly an excellent find.