There are a wide variety of libraries available for research in the Washington, D.C. metropolitan area. In addition, the Internet makes other libraries as far away as England and Australia available. Listed here are the most important ones, through which you can start your research and jump to other resources, online or otherwise.
The Edward Bennett Williams Law Library web page and catalog are the first stops in research. The Library's web pages will allow you to access a number of online subscription databases, such as First Search (worldwide catalog of materials in libraries), African American Biographical Database, America: History & Life (primary index for research in American history), Archives USA, HarpWeek (full text of Harper's Weekly from the Civil War era and early years of Reconstruction), Historical Abstracts, Historical Newspapers Online, Index to Legal Periodicals and Jstor ( full-text backfiles of scholarly journals in the fields of history, philosophy, political science and others), and many others.
The Lauinger Library at the Main campus at Georgetown University is open to Georgetown University Law Center students, staff and faculty. You can check out materials from the library, and go to the library much as you access the Edward Bennett Williams Law Library, but there are separate circulation and access policies governing Lauinger Library. Ask for information about checking out books at Access Services in the Law Center Library, or access their Library web page.
The Library of Congress Law Library, Manuscripts Division and Periodicals Reading Room are all in the Madison Building of the Library of Congress (building closest to the Orange Line Metro stop). The Law Library contains much of the same materials at Georgetown, but they also have some rare books and manuscripts that are unavailable elsewhere. The Manuscripts Division houses many special collections of papers and manuscripts related to the history of the United States. The Periodical Reading Room includes many historical newspapers and journals on microfilm and microfiche that are unavailable elsewhere. All three divisions have many reference and research specialists who can help. In addition, there are other reading rooms that can be valuable resources in your research: The main Reading Room and Reference alcoves in the Jefferson building, and the Social Sciences Reading Room in the Adams building. Books may not be checked out, and must be requested ahead of time. Waiting times for requests can often be as long as 2 hours, especially on weekends. Call ahead, or do some preliminary research at Georgetown with a reference library first, before going to the Library of Congress.
The National Archives and Records Administration (NARA) is responsible for collecting, preserving and making available the records of the Federal government, including all three branches of government, agencies, and offices. There are two main facilities in the Washington Metropolitan area: Archives I, which is the old building at Pennsylvania Avenue, N.W., between 7th and 9th Streets, and Archives II, which is a group do 5 buildings on a campus near the University of Maryland at College Park. In addition, NARA oversees the Presidential Libraries and Federal Records Centers, scattered throughout the U.S.
The Archives I building is currently undergoing major renovations but the research rooms remain open to researchers. The Archives I building houses textual and microfilm records relating to genealogy, American Indians, pre-Word War II military and naval-maritime matters, the New Deal, the District of Columbia, the Federal Courts, and Congress. The Archives II buildings at College Park, Md. houses cartographic and architectural records, motion pictures and non-textual records, audio and video recordings, still pictures and electronic records, as well as the Nixon Presidential materials, the John F. Kennedy Assassination Records Collection, the Berlin Documents Center microfilm, and textual records from most civilian agencies and military records since World War II. A shuttle bus links the two archives sites and is free to researchers. The Archives II College Park site has free parking.
The best guide to the National Archives materials is the official Guide to Federal Records in the National Archives of the United States, compiled by Robert B. Matchette, et al., in 1995. It is available in the Georgetown Law Library in the Reference Department, and online at the NARA official web site: http://www.archives.gov/research/guide-fed-records/. The online version can be difficult to use, if the researcher does not understand how archival records are organized. There is also ARC, the Archival Research Catalog, the online catalog of NARA's nationwide holdings:
The University of Texas at Austin Law Library Rare Books and Special Collections Department has a pretty good Guide to Legal History Resources on the web. Its emphasis is on U.S. legal history, and Texas legal history in particular, but it is a good links page to start from as well.
Although the United States Supreme Court Law Library is closed to most researchers, they do have resources online that can be of use. Exceptions are sometimes made by the Law Librarian at the Supreme Court if materials are unavailable anywhere else, and the research is of importance to the history of the Supreme Court. Make an appointment with the Special Collections Librarian to determine if the library will be open on a limited basis.