ICLEI is a membership association of local governments and national and regional local government associations that have made a unique commitment to sustainable development. ICLEI is made up of 1029 local governments, representing over 400 million people worldwide.

ICLEI is a democratic organization with each local government Member holding a position on the Council. The Members of the Council establish ICLEI's priorities and direction through the adoption of the Strategic Plan. Members also elect 21 representatives to serve on the Executive Committee, which oversees the implementation of the Strategic Plan and ICLEI operations.

ICLEI offers local governments and their national and regional associations Full Membership in the Council with powers to govern the organization internationally. Membership rates are based upon the population of the local authority and its national per capita income. The payment of dues is made on an annual basis.

ICLEI also offers non-voting Associate Member status to state and national government agencies, non-profit and non-governmental organizations, and individuals who wish to be involved in the organization's ongoing efforts.