This paper provides a historical literature review of the subject librarian position. The subject librarian position was originally created to support patrons in specific subjects. Since the position's creation, a subject librarian's foundational duties have consisted of collection development, reference, instruction, and liaison. Though liaison work has received increased emphasis, the subject librarian duties have been remarkably consistent through time. "Subject specialist" or "subject librarian" have been the most commonly used titles for the position, though recently "liaison" has become more common. The subject librarian position has persisted because it provides an important human connection to the library and because it is flexible and adaptive to change. Subject librarian positions vary in different libraries because each adapts the position to meet their needs.