Tamarind Institute has been around since its founding in Los Angeles in 1960 (they became part of the University of New Mexico in 1970) . They are a nonprofit center for fine art lithography.
Lithography is a type of chemical printing using a smooth surface to do the printing (as opposed to a carved one). Originally lithographs were made with stone. Now you often see them made with aluminum. Lithography is often used to recreate an existing painting as a print but it is also a process used in creating original works. The website linked above is a great place to find out more.