In Cambodia the currency is the riel. However, the Cambodian economy being what it is, locals prefer getting paid in dollars since they get more value from it than from their own currency. I made the mistake of exchanging a bunch of cash, losing money in the process, which I didn’t really need to do. Local restaurants and shops will accept riels, but it’s easier and ultimately cheaper for you to just use American currency. Do bring lower value bills though, lots of $1, $5 and $10 bills will serve you well. American coinage is not used, so try to have even transactions or you’ll be stuck with a lot of nearly useless riels.