The free movement of persons is a fundamental right guaranteed by the EU to its citizens. It entitles every EU citizen to travel, work and live in any EU country without special formalities. Schengen cooperation enhances this freedom by enabling citizens to cross internal borders without being subjected to border checks. The border-free Schengen Area guarantees free movement to more than 400 million EU citizens, as well as to many non-EU nationals, businessmen, tourists or other persons legally present on the EU territory.

Reference: http://ec.europa.eu/dgs/home-affairs/what-we-do/policies/borders-and-visas/schengen/index_en.htm