In the United States a public library is established under state enabling laws or regulations to serve a community, district, or region, and provides at least the following:

an organized collection of printed or other library materials or a combination thereof;

paid staff; an established schedule in which services of the staff are available to the public; the facilities necessary to support such a collection, staff, and schedule, and

is supported in whole or in part with public funds.

There may be only one public library in a community or there may be a public library system. Just as a school system has elementary and secondary schools, a public library that administers a branch, a bookmobile, a central library, and/ or a books-by-mail service is called a public library system.

A central library may be the only one public library in a community or it may be the library which is the operational center of a public library system. Usually all processing is centralized here and the principal collections are housed here. A central library is synonymous with a main library. A public library system does not have more than one central library.

A branch library is a library within a library system which has at least all of the following: separate quarters; an organized collection of library materials; paid staff; and regularly scheduled hours for being open to the public.
 
A bookmobile is a traveling branch library. It consists of at least all of the following:
 
A truck or van that carries an organized collection of library materials;
paid staff; and regularly scheduled hours (bookmobile stops) for being open to the public.

Books-by-Mail is a direct mail order service which provides books and other library materials. Books-by-mail typically serves rural residents, the disabled, the homebound, and others without access to a public library. Requests for materials are usually received by mail and by telephone only.

Source: National Center for Education Statistics  http://nces.ed.gov/surveys/libraries/public.asp

State Libraries

One for the District of Columbia and another 50; one for each 50 states  State Library Agencies are the official agencies charged with state-wide library development and the administration of federal funds authorized by the Library Services and Technology Act.

These agencies vary greatly. They are located in various departments of state government and report to different authorities. They are involved in various ways in the development and operation of electronic information networks. They provide different types of services to different types of libraries. StLAs are increasingly receiving broader legislative mandates affecting libraries of all types in the states (i.e., public, academic, school, special, and library systems). For example, their administrative and developmental responsibilities affect the operation of thousands of public, academic, school, and special libraries in the nation.

StLAs provide important reference and information services to state government and administer the state library and special operations such as state archives, libraries for the blind and physically handicapped, and the State Center for the Book.

The StLA may also function as the state's public library at large, providing service to the general public and state government employees. Data on StLAs complement NCES data collected on public, academic, and school libraries

Source: http://nces.ed.gov/surveys/libraries/state.asp

IMLS is the primary source of federal support for the nation’s 122,000 libraries and 17,500 museums.

The Institute's mission is to create strong libraries and museums that connect people to information and ideas. The Institute works at the national level and in coordination with state and local organizations to sustain heritage, culture, and knowledge; enhance learning and innovation; and support professional development.

The IMLS role is to provide leadership and funding for the nation’s museums and libraries, resources these institutions need to fulfill their mission of becoming centers of learning for life crucial to achieving personal fulfillment, a productive workforce and an engaged citizenry.
IMLS supports several activities, including Library Services and Technology Act (LSTA) in which goals are

• To promote improvements in library services in all types of libraries in order to better serve the people of the United  States

• To facilitate access to resources and in all types of libraries for the purpose of cultivating an educated and informed citizenry; and

• To encourage resource sharing among all types of libraries for the purpose of achieving economical and efficient delivery of library services to the public

http://www.imls.gov/about/about.shtm

2007