Costa Rica adoptions fall under the Hague Convention. This adds 2 new sections in the Immigration and Nationality Act. More info is available at INS site.
Other countries that fall into this category:
Andorra, Australia, Austria, Brazil, Burkina Faso, Burundi, Canada, Chile, Colombia, Costa Rica, Czech Republic, Cyprus, Denmark, Ecuador, El Salvador, Finland, France, Georgia, Iceland, Israel, Italy, Lithuania, Mauritius, Mexico, Moldova, Monaco, Netherlands, New Zealand, Norway, Panama, Paraguay, Peru, Philippines, Poland, Romania, Spain, Sri Lanka, Sweden, and Venezuela.