This article is from the Libraries FAQ, by Anthony Wilson firstname.lastname@example.org with numerous contributions by others.
The U.S Bureau of Labor Statistics, http://stats.bls.gov/ , maintains
a database of job descriptions and career outlooks. This is a helpful
place to start when researching career options:
Library Assistants and Book Mobile Drivers
Also, the Library Support Staff Resource Center provides descriptions
of the various roles played by library personnel, plus links to more
information on work roles:
The following is from the Libraries FAQ 1.2 by Steve Bergson:
In 1927, "The Report of the Bureau of Public Personnel Administration
submitted to the Committee on the Classification of Library Personnel
of the American Library Association proposed 'a separation of clerical
from non-clerical duties.'" [Baker, P. (1986) _What About the
Workers?: Study of Non-professional Staff in Library Work_. London:
Association of Library Assistants, pg.2]. Shelvers are the minimum
wage teenagers (usually) who shelve the materials after they have been
returned. Library assistants or technicians might do any of the
following: shelving (in the absence of shelvers), circulation duties
(check in, check out, supervision), derived cataloguing, programming,
ordering, answering ready reference questions or materials processing.
Librarians might do any of the following professional tasks: book
selection, original cataloguing, making library policy, evaluating
performance of others, answering more complex reference questions,
ordealing with the complaints and concerns of patrons. Librarians may
do nonprofessional tasks in the absence of technicians and shelvers.
Library technicians and assistants may do professional tasks in the
absence of professional staff.