Activities in the various astronomical sub-discplines are mostly coordinated through the 11 IAU Scientific Divisions. These Divisions act as umbrellas for one or more IAU Commissions, each focusing on a narrower scientific or organisational theme.

Divisions

• Division I Fundamental Astronomy
• Division II The Sun & Heliosphere
• Division III Planetary Systems Sciences
• Division IV Stars
• Division V Variable Stars
• Division VI Interstellar Matter
• Division VII Galactic System
• Division VIII Galaxies and the Universe
• Division IX Optical and Infrared Techniques
• Division X Radio Astronomy
• Division XI Space and High Energy Astrophysics

Commissions

A few Commissions have been given the charge by the Executive Committee to oversee matters related to the health of astronomy worldwide - Commissions of the Executive Committee - or cover subjects ranging across all astronomical disciplines. These Commissions are not included in the above structure of Scientific Divisions.

Finally, Working Groups have been established by the Executive Committee, by Divisions, or by Commissions, to undertake certain well-defined tasks for certain periods. Among these, the Working Groups of the Executive Committee undertake essential functions on behalf of the IAU as a whole.