“Deposit”, just as it implies, means authorized storage. In order to publicize and promote its document information resources, United Nations set up the depository library system in 1946. One or more libraries from many countries and regions, open to the public, are chosen as the UN depository libraries. They are responsible for collecting, managing and providing lending service to readers. The Dag Hammarskjöld Library (DHL) takes in charge of distribution of UN important documents and publications within the scope of designation. The DHL along with other member libraries constitute the UN depository library system.

　　By March 2010, the UN has designated 405 depository libraries in 146 countries and regions. China is one of the earliest countries joined in the UN depository library system, and the National Library of China has formally become its depository library in 1947, more than 60 years until now. At present, there are 20 depository libraries in China, and the amount is the second most in the world.