Professional law librarians
A professional law librarian, whether at a firm or at a law school, holds a Masters degree in library and information science and frequently will also have a J.D and/or other advanced degrees. (Some firms employ someone they call a "librarian" who does not have such qualifications, but instead is essentially a caretaker of the physical library.)
The role of a firm librarian varies widely from firm to firm. Many top firms have a staff of research librarians who bill their time to clients and produce research memos on a regular basis. In contrast, some firms do not employ any professional librarians, and offer no library-based services at all. Often librarians are responsible for fact-oriented or law-related research rather than legal research per se . Accordingly, librarians may conduct research to identify expert witnesses, obtain corporate intelligence, obtain facts for trial exhibits, and much more. As a rule, such research librarians engage in research projects for senior associates and partners, and are generally not available to perform research for junior associates and summer associates. (In some cases, their billing rate may be as high as yours.) However, they will almost always be amenable to providing you with advice about research sources and strategies.
In addition to conducting research and providing research advice, firm librarians often produce web pages within your firm's intranet that provide research guides, links to key databases, and other helpful information.