How to pay in Costa Rica?

The currency of Costa Rica is the Colón.

The current exchange rate (June 2015) is around 530 Colón per USD. It is helpful to always have both currencys (USD/Colón) with you. Hotel, trips, taxes and entry fees of national parks possible to pay in USD. Supermarkets, shops, gas-stations, restaurants, etc. prefer the Colón.

We recommend, always paying in the currency, whichever displayed on the bill. Otherwise you might get a bad exchange rate and it is common to receive Colónes, when you, for example, pay USD instead of Colónes in a supermarket.

Important note: Please do not change (large amounts of) money at the airport, you will get an awful exchange rate. 
The best way is: Withdrawing money from the ATM, you can get USD and Colónes.
It is also very common to pay with a credit card. Also nearly every bank changes the Euro, but to a bad rate.