The American Library Association has defined the professional and the supportive categories of library personnel since 1970 and revised their statement in 1976. For each level are two titles. One is for positions that have library-related qualifications and the other is for nonlibrary-related qualifications. There are two levels which are considered professional levels and then three which are considered supportive.
The top level is the Senior Librarian. The nonlibrary-related equivalent is Senior Specialist. The basic requirements include relevant experience as well as education beyond the M.A, or any other Master's level degree, for example, a master's degree in any of its different designations like M.A., M.L.S., M.S.L.A., M.Ed., and so on. This means they have a post master's degree; a Ph.D. perhaps. They also have continued their education in many forms of relevant information. The nature of the responsibilities for senior librarian or specialist are the top-level responsibilities. This includes but is not limited to administration. They have superior knowledge of some aspect of librarianship, or of other subject fields of value to the library.
The other professional level is called librarian, or specialist. You must have a Master's degree for this category. Their responsibilities include management. This requires independent judgment and interpretation of the rules and procedures. Librarians must be able to analyze the problems of the library and come up with original and creative solutions for them. They normally utilize the knowledge of the subject field that is represented by their academic degree.
On the supportive, or paraprofessional level, the top level is Library Associate. The nonlibrary-related title is Associate specialist. The basic requirements include a bachelor's degree that may or may not have course work in library science. A bachelor's degree with additional academic work short of the master's degree also falls into this category. The Associate level has a high level of supportive responsibilities. They normally work within the established procedures and techniques. They usually work under some supervision by a professional, but they require judement, as well as subject knowledge such as is represented by a full, four-year college education that culminates in the bachelor's degree.
The next category is the Library Technical Assistant, or Technical Assistant. This requires either at least two years of college-level study or an A.A. degree that may or may not include Library Technical Assistant training, or postsecondary school training in relevant skills. Technical Assistants perform tasks that are supportive to Associates and higher ranks. They follow established rules and procedures that include , at the top level, supervision of such tasks.
The lowest category is a clerk. This has the basic requirements of business school or commercial courses that are supplemented by in-service training or on-the-job experience. Clerical assignments are required by the individual library.
Introduction to Library Public Services, Sixth Ed., By G. Edward Evans, Anthony J. Amodeo, and Thomas L. Carter.