A passport is required to get into Costa Rica. Citizens of the US, Canada, Great Britain, and most other European nations can stay as a tourist for 90 days. Citizens of New Zealand, Ireland, and Australia may stay for 30 days but may have the option to extend their stay once in the country. If you want to stay longer than the normal allowable time the easiest thing to do is to cross into Panama or Nicaragua for at least 72 hours. Then you may re-enter the country on another tourist visa. Although there are some people who have used this method to stay in Costa Rica for as long as 15-20 years be warned--there are rumors that the government may be cracking down on long-term "tourists" to reciprocate for tightening border policies in the US. The worst case scenario is that you would be denied re-entry.