If you’re not from Europe you can’t get one. The reverse works for Eurail.

You must be a legal resident of a European country for 6 months to get an Interrail pass, so you might qualify if you’re on a student or work visa.  I think the price varies depending on which country is your country of residence (it’s more expensive if you’re a resident of a richer country with higher rail prices).  Interrail passes are honored in more countries, but they usually aren’t honored on the premier and express trains. 

Eurail passes (as Feicht says, for folks who are not residents of Europe) are honored on all trains run by the national rail service in the member countries — although you have to pay extra for the required reservation on express and premier trains and (rarely) have to pay a supplemental charge on the fanciest premier trains.