ICSU currently has 31 Scientific Union Members and 121 National Scientific Members covering 141 countries. In addition, ICSU has 23 International Scientific Associates.
There are two categories of full Members:
Of the 121 National Scientific Members 91 are full National Scientific Members, 8 are National Scientific Associates and 22 National Scientific Observers. National Scientific Associates are potentially qualified, but not yet ready, for full membership and National Scientific Observers are those Members which have failed to fulfil their financial obligations.
A National Scientific Member adheres to ICSU either through its principal scientific academy, or its national research council, or any other institution or association of institutions effectively representing the range of scientific activities in a definite territory and which has been in existence for at least four years. National Scientific Associates and National Scientific Observers have no vote.
International Scientific Unions
The Scientific Unions are international, non-governmental, professional organizations devoted to the promotion of activities in a particular area of science, and have been in existence for at least six years.
Scientific Associates are organizations that work in areas related to ICSU's priorities and activities, and whose scientific activities do not fall primarily within the scope of a single Scientific Union Member. Scientific Associates must have been in existence for at least six years and have no vote.