The Astronomy Digital Library provides access to astronomical literature and to on-line data. The Astrophysics Data System (ADS) is the literature search system and archive in this library. It is a NASAfunded project and access to all the ADS services is free to everybody world-wide. The ADS Abstract Service allows the searching of four databases with abstracts in Astronomy, Instrumentation, Physics/Geophysics, and the ArXiv Preprints with a total of over 2.9 million references. The system also provides access to reference and citation information, links to on-line data, electronic journal articles, and other on-line information. The ADS Article Service contains the full articles for most of the astronomical literature back to Volume 1. It contains the scanned pages of all the major journals (Astrophysical Journal, Astronomical Journal, Astronomy & Astrophysics, Monthly Notices of the Royal Astronomical Society, and Solar Physics), as well as most smaller journals back to Volume 1. There are now 10 mirror sites of the ADS available in different parts of the world to improve connectivity. The ADS can be accessed through any web browser without signup or login at: http://ads.harvard.edu/.