The official currency of Thailand is the Thai BAHT (pronounced - bart). 

One baht is divided into 100 satangs.

Coins come in denominations of: 1, 2, 5 and 10 baht, as well as (rarely seen or used) in 1, 5, 10, 25 and 50 satang.

Paper Notes come in denominations of: 20, 50, 100, 500 and 1,000.

The most commonly used coin is the 10 baht and the most commonly used note is the 100 baht.

*There are still some old 10 baht notes in circulation, and you may even encounter a special "Commemorative issue" 60 baht note. It is reported that the 50 baht note is being phased out of general circulation.

Thailands Baht and a street cash exchange (forex) booth

Chiang Mai Airport and Bangkok Airport Cash Exchange (forex) booths

• Travelers Cheques are generally accepted only at dedicated foreign exchange shops or banks. 
  
• Automated Teller Machines (ATM's) are plentiful throughout Thailand, and most will accept cards issued by any of the major international banking networks (Plus, Cirrus, etc.)

Be aware that from April 17 2009, most foreign debit and credit card withdrawals from a Thai ATM's MAY incur a 150 baht fee levied by the local ATM owner, in additon to any fee assesed by your home financial institution.   Extra ATM fee announcement - PDF file

• Major credit cards such as Visa, Mastercard, JCB and American Express, are readily accepted at most hotels, airlines, restaurants and upscale merchants.
  

• To prevent your credit/debit card from being declined, it is important to advise your card issuer of your travel plans in advance.
  
• Some insitiutions routinely block/deny unexpected charges from Thai merchants for fear of possible fraudlent use.

Exchanging cash in Thailand is EASY 

FOREX (FOreign EXchange)  booths are very common and clearly post their daily exchange rates on an electronic notice board.

• Cash exchanges in Thailand incur NO commissions or fees.
  
• Do not buy any Thai currency until you arrive in Thailand.
  
• The rates offered in Thailand are ALWAYS BETTER than you could get back home.
  
• FOREX booths accept ALL MAJOR currencies.
  
• DO remember to bring ONLY bank notes in good overall condition.
  
• FOREX booths generally WILL NOT accept bank notes that are torn, ripped, damaged or are excessively marked/stamped.

Which is best for me?;

Cash

• There are NO fees or charges to bring your home currency, and NO fees or charges to exchange it into Baht in Thailand .
  
• It's the easiest to use, and in most cases the cheapest as well, but has obvious risks associated with loss.
  
• You do not have to present ID to exchange foreign currency.
  
• Make sure you count your money for clerical errors BEFORE you walk away from the exchange counter.
  
• Again, you do not need to acquire any Thai baht BEFORE arriving in THAILAND.

At Bangkok's Suvanabumi Airport, there are exchange booths right in the Customs Hall (after clearing Passport Control, in the baggage claim area) as well as in the general arrivals area. ATM's are also readily available in the airport. Rates of exchange are the same at both city and airport exchange locations. There is no advantage to waiting until you arrive in town and they are open 24 hours a day (just like the Airport).

If you prefer the security offered by Travellers cheques, then take them in your home currency if available. i.e. If you're from Britain, don't get US$ cheques or you'll lose money on that exchange before you've even started. In some cases there is a fee to buy travellers cheques.

• When you exchange Traveler Cheques in Thailand there is a mandatory THB33 per cheque fee (incl. the THB3 Government Duty).
  
• To minimise this THB33 fee it's wise to get your cheques in larger denominations (i.e. fewer exchanges).
  
• T/C's actually get a marginally better exchange rate than cash, which will help offset part of the tax.
  
• When cashing T/C's you will be required to present your ID (normally your passport).
  
• T/C's provide improved security for you, as they can be replaced if lost/stolen.

ATM

• Most Thai banks are now charging a THB150 fee per withdrawal when you use their ATM.
  
• Your home bank may also levy a fee or fees.
  
• Using ATM's is a safer option than cash and more convenient than T/C's.
  
• This may be an excellent option if your home bank doesn't charge high fees.
  
• ATM's are plentiful and located just about everywhere.
  

*Prepaid Cash Cards - Like ATM's, may also be subject to fees by issuer as well as the local Thai bank ATM.

Remember, you DO NOT need any Thai Baht before your arrival in the Kingdom, to get Thai Baht ahead of time will subject you to a considerably poorer rate of exchange plus probable commission fees.

Exchanging Cash or T/C's at the HOTEL.

• While Hotels DO offer cash and T/C exchange facilities, the rate offered is usually very POOR compared to that offered by Banks/Forex booths.

Dynamic Currency Conversion

• When paying by Credit Card (hotels restaurants shops etc), insist on being billed in Thai baht.
• Being billed in your home currency, (a practice which has become more prevalent recently) involves both a hidden surcharge and bad exchange rates and can add 5% to the nett cost in some cases.
  
• The best advice is to insist on paying the local currency amount.
  
• If you are charged in your home currency, someone is going to make a profit on the deal, and it won't be you.

THE BEST ONLINE SOURCE FOR CURRENT EXCHANGE RATES IN THAILAND

http://bankexchangerates.daytodaydata...

To determine the current rate of exchange of your home currency to the Thai baht, you can check this web site which shows the rates offered by all major Thai banks/FOREX booths.

• Use the first drop down box to insert your home currency.
  
• You can also check ATM rates (option TT), and Travellers Cheque rates (option cheque)
• These rates are exactly what the banks listed are offeroing at this moment.
  

BE RESPECTFUL WHEN HANDLING THAI CURRENCY!

All currency in Thailand, paper and coin, bears a portrait of His Majesty King Bhumibol Adulyadej or a deceased relative.

Remember that Thailand has and does enforce the national lèse majesté laws. These laws expressly prohibit any act - verbal, physical or written, that shows insolent or disrespectful behaviour toward any member of the Royal family.

With this in mind;

• DO NOT EVER step on a coin to stop it from rolling away.
  
• DO NOT step on a Thai banknote to stop it from blowing away.
  
• DO NOT throw a note or coin in anger towards another person. 
  
• DO NOT tear, burn or otherwise deface a note or coin.

These acts can easily been perceived as disrespectful toward his Majesty The King, or another member of the Royal family (and would be highly offensive to any Thai person that witnessed such an occurrence), and in keeping with lèse majesté laws, you may be subject to unpleasant consequences.

Please show respect accordingly.