This document outlines Ezio Manzini's lecture on design in the age of networks and sustainability given in Milano on May 20, 2010. The lecture discusses how individuals and communities are inventing new ways of living more sustainably through local food networks, public spaces, social services, and digital platforms. It argues that social innovation driven by these grassroots solutions is an important driver of sustainable change. The lecture proposes that designers should take a systemic and strategic approach to co-designing tools and enabling frameworks that can replicate and scale up promising local social innovations.