Library Science is practiced by professionals known as librarians. Not every person who works in a library is a librarian, since many staff members perform more technical functions, such as checking library materials in and out and making sure they are re-shelved in the correct places. Librarians, however, are vital in order to manage the collection and to ensure that the information and materials are as complete and appropriate for that collection as possible. Librarians also help patrons to select the materials most suited to their needs.
Libraries themselves date back thousands of years, with perhaps the earliest known collection being one found in ancient Syria dating from around 1200 BC. It's harder to pinpoint when library science as a discipline got its start, but there was an attempt at establishing an early book classification system during the Han Dynasty in ancient China (202 BC-220 AD). Modern library science, at least in the United States, can be said to have had its start in the 19th century with Melvil Dewey, of Dewey Decimal System fame. Not only did he establish this most widely-known of library classification systems, he also established the nation's first librarian training program.
A librarian typically requires a master's degree in library science (MLS) or one in library and information science (MLIS). Persons employed in libraries who do not possess such a master's degree are usually classified as paraprofessionals, and do not perform the same range of duties as do professional librarians.
The American Library Association recognizes libraries in four different categories: public, school (K-12), academic and special. Public libraries are typically community-funded, usually at the county or municipal level, and are open to all area residents. School libraries are found in public and private schools serving children from pre-K through 12th grade. Academic libraries are those attached to colleges and universities. Special libraries can be attached to corporations or other types of organizations such as hospitals or government agencies, or they can be targeted at serving the needs of a particular population or to house a particular type of material.
As libraries expand their holdings into cyberspace, so too must librarians expand their information management skills into the digital realm. The study of library science today is concerned with techniques for online information retrieval, and for providing patron service in a virtual environment. Although most librarians still work in traditional settings, the growth of distance education and digitized special collections points toward a future where many academic and school librarians, as well as some special and even public librarians, will be performing most of their duties online.