A national library is a library

Library

In a traditional sense, a library is a large collection of books, and can refer to the place in which the collection is housed. Today, the term can refer to any collection, including digital sources, resources, and services...

 specifically established by the government

Government

Government refers to the legislators, administrators, and arbitrators in the administrative bureaucracy who control a state at a given time, and to the system of government by which they are organized...

 of a country to serve as the preeminent repository of information for that country. Unlike public libraries

Public library

A public library is a library that is accessible by the public and is generally funded from public sources and operated by civil servants. There are five fundamental characteristics shared by public libraries...

, these rarely allow citizens to borrow books. Often, they include numerous rare, valuable, or significant works.

There are wider definitions of a national library, putting less emphasis to the repository character.

National libraries are usually notable for their size, compared to that of other libraries in the same country.