In 2019, the International Astronomical Union (IAU) is celebrating its 100th anniversary. To commemorate this milestone, the IAU is organising a year-long celebration to increase awareness of a century of astronomical discoveries as well as to support and improve the use of astronomy as a tool for education, development and diplomacy under the central theme "Under One Sky".

The centennial celebrations will stimulate worldwide interest in astronomy and science and will reach out to the global astronomical community, national science organisations, societies, policy-makers, students, families and the general public.

The IAU100 activities will take place at global and regional levels, and especially at the national and local levels. To coordinate the initiative, the IAU has set up the IAU100 Task Force as well as the IAU100 Secretariat based in Leiden Observatory (The Netherlands). The task force has prepared a comprehensive programme of Global initiatives to reach targeted audiences worldwide through the IAU National Outreach Coordinators and National Astronomical Societies, which have set up National IAU100 National Committees to ensure the worldwide success of the initiative.