The Assembly is made up of 60 Assembly Members (or "AMs"), elected by a system of proportional representation called the Additional Member System. 40 of the AMs represent the same constituencies as MPs from Wales; the remaining 20 are elected on a regional basis, with four AMs serving each of 5 regions across Wales. Everyone has two votes in an Assembly election: one for a constituency AM and one for a regional AM.

Following the third elections to the Assembly in May 2007, there are 26 AMs representing the Labour Party, 15 representing Plaid Cymru, 12 representing the Conservative Party, 6 representing the Welsh Liberal Democrats and one independent.