The University Library and the Law Library hold over two million items. The libraries receive 65,000 serials in over 210 databases, provide access to approximately 11,000 electronic books and reference tools, and add over 20,000 physical items annually to their collections. There are subscriptions to all Idaho newspapers and representative papers from around the U.S. The library is a regional depository for U.S. and Idaho state government documents, serves as the statewide clearinghouse for geospatial data, and is a designated Earth Science Information Center.

The libraries’ collections emphasize the land-grant traditions of the basic sciences, agriculture, and the natural resources while maintaining supporting collections in the humanities and social sciences. Special Collections and Archives is rich in collections of Pacific Northwest and Idaho state history, including books, photographs, and historical maps. The archives contain personal papers and records of families, politicians, educators, authors, and business records of lumber companies, mines, and railroads. It is also home to the International Jazz Collections which contains papers, photos, and recordings of jazz musicians and critics. The library has created and is developing digital images of many important resources, providing electronic access to such archives as the International Jazz Collections, the Barnard Stockbridge photographic collection, Idaho Waters Digital Library, historic aerial photographs, and the Kooskia internment camp scrapbook.

The Law Library operates as the laboratory for the College of Law, housing materials that are used to support the academic program of the college and the research interests of law faculty and students. Numbering over 250,000 volumes and volume equivalents, the collection has primary materials, in the form of statutes and court reporters, for the federal system and all 50 states. Secondary materials, consisting of treatises, law reviews, and loose-leaf services, round out the American law collection. There is a working collection of United Kingdom and Canadian primary and secondary materials, and a growing international law collection. The Law Library is also a selective federal documents depository. A variety of electronic legal databases are available for use by the University community and the general public.

The law library’s special collections include records and briefs submitted to the Idaho Supreme Court and Court of Appeals, an historical collection of Idaho legislative and administrative legal materials, and the Clagett Collection, which consists of materials collected by Fred and Dorothy Clagett to support their research on the life and times of William H. Clagett, the president of Idaho's Constitutional Convention in 1889.

The library building was expanded and remodeled in 1993, providing structural opportunities to expand collections in the current facility. The library facility is open from 8 a.m. to midnight daily during the school terms, with a 24-hour study area. The library is home to the largest student computing lab on campus, with nearly 200 computers available to students, faculty, and staff. The emphasis on building electronic collections enables the library to offer services to all students and faculty at all times, regardless of location.

There is a reciprocal use agreement between the University of Idaho Libraries and the Washington State University Libraries located in Pullman, eight miles away, giving students immediate access to the equivalent of library resources in many urban areas. Similar agreements exist with the Lewis Clark State College Library, located in Lewiston, North Idaho College Library, located in Coeur d’Alene, Whitworth University Library and Gonzaga University Libraries, located in Spokane. The library cooperates with institutions throughout the Pacific Northwest and beyond. Electronic delivery services coupled with courier systems ensure rapid delivery of items held throughout the area.