  In this paper we present a number of metrics for usage of the SAO/NASA
Astrophysics Data System (ADS). Since the ADS is used by the entire
astronomical community, these are indicative of how the astronomical literature
is used. We will show how the use of the ADS has changed both quantitatively
and qualitatively. We will also show that different types of users access the
system in different ways. Finally, we show how use of the ADS has evolved over
the years in various regions of the world.
  The ADS is funded by NASA Grant NNG06GG68G.
