Digital technologies and the Internet have transformed many areas of business – from Google and Amazon to Airbnb and Kickstarter. Huge sums of public money have supported digital innovation in business, as well as in fields ranging from the military to espionage. But there has been much less systematic support for innovations that use digital technology to address social challenges. Digital technologies are particularly well suited to helping civic action: mobilising large communities, sharing resources and spreading power. A growing movement of tech entrepreneurs and innovators in civil society are now developing inspiring digital solutions to social challenges. These range from social networks for those living with chronic health conditions, to online platforms for citizen participation in policymaking, to using open data to create more transparency around public spending. We call this Digital Social Innovation (DSI). Over the last 18 months Nesta, funded by the European Commission, has led a large research project into DSI. The project seeks to define and understand the potential of DSI, to map the digital social innovators, their projects and networks, and to develop recommendations for how policymakers, from the EU to city level, can make the most of DSI.