An academic library is a library that is attached to a higher education institution, which supports the curriculum and the research of the university faculty and students. According to the National Center for Education Statistics, there are an estimated 3,700 academic libraries in the United States. Class reading materials, intended to supplement lectures by the instructor and housed in academic libraries, have historically known as "reserves". Before electronic resources became available, the reserves were supplied as actual books or as photocopies of appropriate journal articles. Modern academic libraries provide access to electronic resources.

Academic libraries must determine a focus for collection development since comprehensive collections are not feasible. Librarians do this by identifying the needs of the faculty, student body, the mission and academic programs of the college or university. When there are particular areas of specialization in academic libraries, these are often referred to as niche collections. These collections are often the basis of a special collection department and they may include original papers, manuscripts, artwork, and artifacts written or created by a single author or about a specific subject.

There is a great deal of variation among academic libraries based on their size, resources, collections, and services. The Harvard Library, which houses over 20 million volumes, is the largest strictly academic library in the world, although the Danish Royal Library—a combined national and academic library—has a larger collection at about 37 million volumes. The University of California operates the largest academic library system in the world, managing about 41 million volumes across 100 libraries on ten campuses. Another notable example is the University of the South Pacific which has academic libraries distributed throughout its twelve member countries.

Libraries date back to the ancient world. The earliest academic libraries include the Library of Alexandria and the library at Nalanda University, which apparently burned for months because of the sheer number of manuscripts.

The first colleges in the United States were largely intended to train clergy members. The libraries associated with these institutions largely consisted of donated books on the subjects of theology and the classics. In 1766, Harvard University had the most volumes held followed by Yale University, which had 4,000 volumes. Access to these libraries was restricted to faculty members and a few students: the only staff was a part-time faculty member or the president of the college. The priority of the library was to protect the books, not to allow patrons to use them. In 1849, Yale was open 30 hours a week, the University of Virginia was open nine hours a week, Columbia University four, and Bowdoin College only three. Students instead created literary societies and assessed entrance fees for building a small collection of usable volumes, often over what the university library held.

In 1876, the American Library Association (ALA) was formed with members including Melvil Dewey and Charles Ammi Cutter. Libraries re-prioritized to improve access to materials and found funding increasing due to increased demand for said materials.

In 1904, the Bibliographical Society of America was founded to foster the study of books and manuscripts. Academic librarians were the majority of members.

Academic libraries today vary regarding the extent to which they accommodate those not affiliated with their parent universities. Some offer reading and borrowing privileges to members of the public on payment of an annual fee; such fees can vary greatly. The benefits usually do not extend to such services as computer usage other than to search the catalog or Internet access. Alumni and students of cooperating local universities may be given discounts or other considerations when arranging for borrowing privileges. On the other hand, some universities' libraries are restricted to students, faculty, and staff. Even in this case, they may make it possible for others to borrow materials through interlibrary loan programs.