The University of Louisville library system is a member of the Association of Research Libraries. Louisville’s main library branch is the William F. Ekstrom Library, which opened in 1981. The four-story building finished an expansion in March 2006, which increased its total size to and shelving capacity to over 1.3 million books. It is one of only five universities in the U.S. to have a robotic retrieval system, which robotically places books in humidity-free bins. The University of Louisville libraries were the seventh academic institution in North America to have such a facility.