Spain is a developed country, a secular parliamentary democracy and a constitutional monarchy,[15] with King Felipe VI as head of state. It is a high-income country and an advanced economy,[16] with the world's sixteenth-largest economy by nominal GDP and the sixteenth-largest by PPP. Spain has the twelve-highest life expectancy in the world.[17] It ranks particularly high in healthcare quality,[18] with its healthcare system considered to be one of the most efficient worldwide.[19] It is a world leader in organ transplants and organ donation.[20][21] Spain is a member of the United Nations, the European Union, the Eurozone, the Council of Europe (CoE), the Organization of Ibero-American States (OEI), the Union for the Mediterranean, the North Atlantic Treaty Organization (NATO), the Organisation for Economic Co-operation and Development (OECD), Organization for Security and Co-operation in Europe (OSCE), the World Trade Organization (WTO) and many other international organisations.