What is big data, and what are its potential benefits and risks? The evolving use of large datasets is rarely out of the headlines, prompting intense debate on privacy and security. From medical records through to GPS signals, the ability to collect large amounts of data holds great potential for research, innovation and productivity. It also means that governments across the globe are grappling with the questions posed by the data being harvested – how to handle it, how to govern its use and how it can impact on policy. Drawing on his extensive work on the subject and his passion for open access science, Sir Mark Walport, Chief Scientific Adviser to the UK Government, will look at how we can make sense of the phenomenon of big data in order to reap the benefits.