Iceland has a market economy with relatively low taxes, compared to other OECD countries, as well as the highest trade union membership in the world. It maintains a Nordic social welfare system that provides universal health care and tertiary education for its citizens. Iceland ranks high in economic, democratic, and social stability, as well as equality, ranking third in the world by median wealth per adult. In 2020, it was ranked as the fourth-most developed country in the world by the United Nations' Human Development Index, and it ranks first on the Global Peace Index. Iceland runs almost completely on renewable energy.