Documentalist is a kind of librarian, specializing in assisting researchers in their search for scientific and technical documentation, in the sense that this term was defined by Paul Otlet (called "the father of documentation", i.e. information science) in the first part of the 20th century. The "information explosion" in the decades following World War II led to the establishment of documentalists as a profession, a branch of librarianship.

Sometimes there have been conflicts between "traditional" librarians, working with books, and documentalists, working with online databases. To some degree, Otlet has a following of ideologic rather than professional nature. With the advent of the Internet in the 1990s, online databases are no longer a specialization, and the term documentalist is more seldom used.