A research library is a library which contains an in-depth collection of material on one or several subjects. A research library will generally include primary sources as well as secondary sources. Large university libraries are considered research libraries, and often contain many specialized branch research libraries. Research libraries are established to meet research needs and as such are stocked with authentic materials with quality content. In most cases research libraries are attached to research institutions or organizations.
Research libraries can be either reference libraries, which do not lend their holdings, or lending libraries, which do lend all or some of their holdings. Some extremely large or traditional research libraries are entirely reference in this sense, lending none of their material; most academic research libraries, at least in the U.S., now lend books, but not periodicals or other material.
A research library is often connected to the services of the university related to scholarly communication, such as support for open access journals run by the institution and the operation of an institutional repository, as well as support for the usage of other institutions' repositories and open archives through discovery tools and academic search engines like BASE, CORE and Unpaywall.