The rule for a US licence
Costa Rica accepts a valid US driver's license for the duration of a standard tourist stay, up to 90 days. No IDP is required.
Beyond 90 days you would need to address local licensing, but that is outside the scope of a normal visit.
Live in Costa Rica?
A licence issued in Costa Rica is what you drive on at home - an IDP translates a foreign licence, so it does not apply to you here. If your licence is from somewhere else, check that licence country: the rule depends on where the licence was issued, not only on where you are driving.
At the rental counter
Costa Rican rentals require mandatory local liability insurance, which is why quoted rates often rise at the counter. A 4x4 is worth having for unpaved routes.
What the permit covers
An International Driving Permit is a translation of your licence into a standard multilingual booklet, issued under the 1949 and 1968 road traffic conventions. It is not a licence, and it is never valid on its own: you carry it with your own licence, and police expect to see both.
It is issued against the vehicle classes already on your home licence, and it never adds one. If your licence does not cover motorcycles, an IDP does not let you ride a scooter in Costa Rica; if it does not cover a heavier vehicle, the permit will not cover a camper or a minibus either. The permit restates what you already hold, in a form the local authorities can read.
Driving in more than one country?
Check every destination on your trip at once - Costa Rica is already filled in.
Check your tripOther destinations
Informational only, not legal advice. Requirements change and vary by length of stay, rental company, and vehicle class. Always confirm with the destination's embassy or your automobile association before you drive.