The building has five floors above ground and two basements. Each floor has a large reading room in the center with desks, group study rooms, lockers and shelved reference works. The reading room on floors two and three is connected by a small atrium. The reading rooms are separated from the stacks, located on the west side of the building, so that the stacks can be maintained at lower temperatures, which are more amicable to book conservation. 250 faculty studies line the east side of the building.
The Regenstein's overflowing collection posed spatial problems to the book stacks. In May 2005, the University of Chicago's Board of Trustees authorized funding for a $42 million dollar addition to the library, which is scheduled to be completed at the end of 2009. The addition will allow the library to maintain physical copies of materials available online while creating space within the book stacks to accommodate approximately 20 years of new print acquisitions. In February 2006, the University's Board of Trustees selected and approved Chicago-based architect Helmut Jahn as the architect for the addition.
The Regenstein Library is a popular social space for the University of Chicago college students: "On our campus, it's not the football game that draws the biggest crowd, it's evening study in the library," said former Provost Richard Saller. "We're a campus where the library is sort of the social center because it is the focus [of the university]." During final week of Winter Quarter, the University of Chicago track team streaks through the Reg, much to the delight of students and the chagrin of the library administration. On the Friday night before Finals Week, students from the Snell-Hitchcock dormitory play a modified version of hide-and-go-seek in the book stacks. Some dorms will occasionally have parties in the stacks, sometimes called "Keg in the Reg" parties.
The Regenstein Library is also the location of the Special Collections Research Center, which houses rare book collections, manuscripts, and university archives. The SCRC was established in 1953 by Herman H. Fussler and was moved to the "Reg" when it opened in 1970. The rare books collection currently holds approximately 265,000 volumes.
The Regenstein is currently undergoing a renovation of its HV/AC system, thus the large section of missing ceiling tile near the stairwell on every floor.