This paper starts by making the case for why a data revolution is needed, highlighting the parlous case of data globally, nationally and locally, focusing on social data, and stating why the gaps matter and how they should be plugged (Sections 1 to 3). Next, it discusses the innovative ways in which data are already being produced and used (Section 4). Finally we set out a vision for a fully- edged revolution, with an examination of outstanding challenges (Sections 5 and 6). Throughout, the paper highlights examples of a range of different uses for big and small data that are being piloted around the world. Some projects are already improving people’s lives, while others are still works in progress. But they demonstrate that the data revolution is already underway.