|The National Diet Library has two origins: one origin is the libraries of the House of Peers and the House of Representatives in the former Imperial Diet established in 1890; and the other origin is the Imperial Library established in 1872 under the Ministry of Education. As the Imperial Library was a pre-war depository library established by law, it had a comprehensive collection of materials published in modern Japan from the Meiji Era. Most of these collections were transferred to the present National Diet Library and formed the basis of the current collection. Prior to the establishment of the modern National Diet Library, the Speaker of the House of Representatives and the President of the House of Councilors invited an U.S. library mission to Japan in 1947. Based on the advice of the U.S. library experts, a basic NDL plan was drawn up which eventually led to the National Diet Library Law. In June 1948 the National Diet Library was opened to the general public with a stock of about 100,000 books originally intended for the two Houses, using the Akasaka Detached Palace (now the Guest Palace). In 1949 another one million books stacked in the former National Library at Ueno, Tokyo (now the International Library of Children's Literature) were added to the NDL's stock. The NDL's primary function is to assist Diet Members to perform their duties. At the same time, it has a mission to provide library services for the executive and judicial branches of the national government and for the general public. As the only depository library in Japan, the Library acquires all materials published in Japan, preserves them as national cultural heritage, compiles catalogs of these publications in a database or other format, and with these collections provides library services.