The contributors provide an overview of theoretical perspectives, methodologies and instructive experiences from all continents, as well as implications for collective action and policy. They argue strongly for social innovation as a key to human development. The Handbook defines social innovation as innovation in social relations within both micro and macro spheres, with the purpose of satisfying unmet or new human needs across different layers of society. It connects social innovation to empowerment dynamics, thus giving a political character to social movements and bottom-up governance initiatives. Together these should lay the foundations for a fairer, more democratic society for all.