The GPM is founded as a universal body to which mayors of all cities—north and south, large and small, rich and poor—are invited to join as members. Its members are mayors of cities and their metropolitan regions or agglomerations. Membership is on an individual basis and limited to mayors only.

The desired minimum population is 250,000, but cities with fewer residents are welcome to join the GPM in “regional coalitions” of several smaller cities with a collective population meeting the threshold. These coalitions may select a mayor to represent them on the GPM floor.

Metro regions on the high end of the population scale are also welcome. Knowing how diverse the boundaries of cities around the world can be, and how municipal and national officials are increasingly choosing to create larger metro-regional districts to facilitate integration of and cooperation between urban, suburban, ex-urban and local agricultural and water regions around city centers, we leave it to participating members to determine the appropriate boundaries for the cities they wish to see represented.

In order to facilitate regular participation of cities around the globe, the GPM works with a virtual platform where mayors participate in interim assemblies on interactive screens without leaving their city hall offices. Given the thousands of cities that could eventually become members, the GPM may decide to establish new forms of representation that permit all cities to participate via federalized or regionalized urban conurbations, or through principles of staggered or even randomly chosen representatives. Not every member will necessarily sit in every annual parliament, but all will be represented permanently – and of course have the opportunity to take part in all virtual sittings.

Mayor Van Aartsen (Chairman Steering Committee) signs the Call to Action, September 11, 2016