As social, economic and environmental challenges increase, the path leading to development and sustainability is seriously jeopardised and the implementation of avant-garde tools and practices urges. This volume aims to shed light on the transition that our society has been passing through and how we can drive this transition towards what we value. It is precisely in these transitional phases that the answers we are looking for come to surface: this is the case of social innovation. This relatively recent concept over the last years gained increasing relevance and interest. This volume explores the complexity and the criticality of both the notions of social innovation and sustainable development through the lenses of an analytical investigation of their meanings and nuances and examines their processes and practices. This volume clearly frames these notions and emphasises the peculiarities and the qualities that foster a nurturing relationship between social innovation and sustainable development.