The American Association of Variable Star Observers (AAVSO) is the largest organization of variable star observers in the world, with members in 42 countries. The purpose of the AAVSO is to coordinate variable star observing, done primarily by amateur astronomers, evaluate the accuracy of these observations, compile, process and publish them, and make them available to researchers and educators around the world. Over 6.5 million observations of variable stars have been complied since the AAVSO was founded in 1911. Those since about 1960 are in computerized form, and it is intended to have all observations in this form within the next year. About 250,000 observations are submitted to and archived by the AAVSO each year, over half of them from outside the USA. Most of the observations are visual, but there is also an active photoelectric program which concentrates on semi-regular and irregular stars such as small-amplitude red variables. In 1990, over 200 requests for AAVSO data and services were received from researchers and educators; this number has increased by a factor of 10 in the last two decades.