I will be traveling to THAILAND for business for 3wks. Do I need a business visa?

If you can avoid it, Just say you are visiting for tourism or pleasure.

You'll have a much easier time. That's what I always say. Even if I am visiting on business.

You can get away with entering Thailand without a visa for 30 days. As to whether or not you'll need a visa for your business trip, it can depend on what kind of business activities you are engaging in.

If you are going to Thailand to attend meetings or seminars, you won't be risking anything by going without a business visa.

If you are engaging in any form of trade, you might be able to get away without having a business visa, but technically you should have one, especially if a transaction is occuring between you (directly) and another party while you are in Thailand. This included any form of consulting work/ temporary employment.

Will you be working here? As in working for a Thai company and being paid by them? I believe that would be the criteria -

I used to come as an importer and purchase items here and i did not need a business visa for that...

but since you will only be here for 3 weeks and can enter on a 30 day entry visa given to most westerners at the airport depending on your country of origin, that should suffice - -

Check Thailand's Visa requirements below.

Call the embassy.

Unless you are carrying commercial samples in your luggage, it will be much less hassle just to pretend you are on a tourist trip. The immigration will not normally spend more than a few seconds on you...

However, this is not a complete answer, as you do not give your Nationality and, unlike the other reply, I am not going to automatically assume you are an American!

A very useful visa site (which ALL airlines use) is

http://www.nwa.com/services/timatic.html

Business Visa requires a little bit more than tourist visa, like letter from your company and or company or business events you're attending but it sure is better than tourist visa.

go to the US government state department site and check the requirements for entry

Penicillin, too.