The Library of Congress (LOC) is a research library in Washington, D.C., that serves as the library and research service of the U.S. Congress and the de facto national library of the United States. Founded in 1800, the library is the United States's oldest federal cultural institution. The library is housed in three elaborate buildings on Capitol Hill. It also maintains a conservation center in Culpeper, Virginia. The library's functions are overseen by the Librarian of Congress, and its buildings are maintained by the Architect of the Capitol. The Library of Congress is one of the largest libraries in the world. Its collections contain approximately 173 million items, and it has more than 3,000 employees. Its collections are "universal, not limited by subject, format, or national boundary, and include research materials from all parts of the world and in more than 470 languages".

A research library is a library that contains an in-depth collection of material on one or several subjects. A research library will generally include an in-depth selection of materials on a particular topic or set of topics and contain primary sources as well as secondary sources. Research libraries are established to meet research needs and, as such, are stocked with authentic materials with quality content. Research libraries are typically attached to academic or research institutions that specialize in that topic and serve members of that institution. Large university libraries are considered research libraries, and often contain many specialized branch research libraries. The libraries provide research materials for students and staff of these organizations to use and can also publish and carry literature produced by these institutions and make them available to others. Research libraries could also be accessible to members of the public who wish to gain in-depth knowledge on that particular topic.