We recommend getting a small amount of local currency before you arrive.
You will typically get a better exchange rate for Thai baht when you are in Thailand, so we recommend getting a small amount of local currency before you travel then getting the rest once you’ve arrived.
There are numerous bureaux de change and currency exchange booths around Koh Samui, however you will need a passport when exchanging foreign currency for Thai baht.
ATMs tend to offer better rates than most currency exchanges, so this is the cheapest and most convenient way of getting local currency in Koh Samui. ATMs accept most credit and debit cards, and you can find them at dozens of locations on Koh Samui.
Most shops and restaurants accept payment by credit or debit card, although often apply a surcharge. For this reason we’d advise paying in cash rather than handing over your debit or credit cards when you are paying for things in Thailand.