The typical library staff consists of three levels of employees: professional librarians, supporting staff and assistants. The proportion of each of these in any given institution depends on the type of library, its budget, and the types of users it serves. Professional librarians usually constitute the smallest number of a library’s employees. In addition to their managerial work, professional librarians assume primary responsibility for providing reference assistance, developing and managing the collections, and overseeing cataloging/classification.

Nonprofessional support staff commonly assumes most of the responsibility for directly serving library users. Their activities include essential functions such as inputting, coding, and verifying bibliographic and other data; ordering library materials; assisting with catalog development; performing circulation duties such as checking out books to users; and performing other services vital to the library’s daily operation.