As of 23 Sep 2016, the World Data System has 99 Member Organizations in four different categories.
The WDS Scientific Committee (WDS-SC) is also in the reviewing process for several other applications. New applications for membership can be started by signing up to the WDS website and filling an Expression of Interest.
Note: Membership requires the signature of a Letter of Agreement (or a similar document) between Members in all categories and ICSU. Template Agreements, in addition to instructions on the procedure, can be found here.
Bylaws detailing procedures regarding WDS membership, interactions between the WDS-SC and WDS Member Organizations, the establishment of Working Groups, WDS biennial Members' Fora, and other practical matters have been developed by the WDS-SC, in consultation with WDS Members. See here for the latest version of the WDS Bylaws.