Singapore is a unitary parliamentary republic with a Westminster system of unicameral parliamentary government. While elections are considered generally free, the government exercises significant control over politics and society, and the People's Action Party has ruled continuously since independence. One of the five founding members of ASEAN, Singapore is also the headquarters of the Asia-Pacific Economic Cooperation (APEC) Secretariat and Pacific Economic Cooperation Council (PECC) Secretariat, as well as many international conferences and events. Singapore is also a member of the United Nations, World Trade Organization, East Asia Summit, Non-Aligned Movement, and the Commonwealth of Nations.