The University of Illinois at Urbana–Champaign (U of I, UIUC, or simply Illinois) is a public research-intensive university in the state of Illinois, United States. It is the oldest, largest, and most prestigious campus in the University of Illinois system. The University of Illinois at Urbana-Champaign is the second oldest public university in the state, second to Illinois State University. It is considered a Public Ivy, and is a long-standing member of the Big Ten Conference and Association of American Universities. The university is designated as a RU/VH Research University (very high research activities). The campus library system is one of the largest public academic collections in the world. It possesses the third-largest university library in the United States (only the collections of Harvard and Yale are larger), and the sixth-largest in the country overall. The university comprises 17 colleges that offer more than 150 programs of study. Additionally, the university operates an extension that serves 2.7 million registrants per year around the state of Illinois and beyond.