The International Astronomical Union: from its first 100 years into the Next Century

The International Astronomical Union was founded in 1919 "to facilitate the relations between astronomers of different countries where international co-operation is necessary or useful" and "to promote the study of astronomy in all its departments." These aims have led the IAU throughout the century of its existence, but the way it has tried to fulfil them has changed. In our book 'The International Astronomical Union: Uniting the Community for 100 Years', Johannes Andersen, Claus Madsen and I traced the changing role of the IAU in the international astronomical community through the twentieth century and into the twenty-first. The IAU has striven - occasionally struggled - to protect international scientific cooperation across the deep political divides that characterized the 20th century. Also, as the science of astronomy changed, the IAU had to find and redefine its role in the rapidly changing international community of astronomers. We especially argue how the emphasis of the IAU's activities has shifted from the first aim - facilitating collaboration by organizing meetings and defining common standards - to the second aim: promoting astronomy by outreach and development programs.