The members of the Union are its Adhering Bodies.

Each Adhering Body forms a National Committee for Crystallography to represent it in the Union. 

Adherence to the Union is in one of the five Categories I-V with corresponding voting powers and contributions.

Regional Associates of the Union are organizations of crystallographers having substantially the same aims and objects as the Union.

Scientific Associates of the Union are international scientific organizations whose interests overlap with the aims and activities of the Union.