The rise of the Internet has made it possible for knowledge to be created and shared in ways that emphasise its character as a common good, rather than as something to be owned. In the world of open source programming, the computer software is distributed under licence, allowing users to change or share the software’s source code - the human readable version of a computer programme. This open and collaborative approach to creating knowledge has produced remarkable results, such as the Linux operating system and the web-based encyclopaedia Wikipedia. In defiance of the conventional wisdom of modern business, open source methods have led the main underlying innovations around the Internet. Other fields have much to learn from open source methods - because they bring principles and working methods which can help to produce better knowledge, goods or services, or make them available on more widely beneficial terms. From the formulation of public policy to more open forms of academic peer review, setting up mutual support groups for people facing similar health problems to collaborative forms of social innovation, the principles of open source promise to radically alter the we approach complex social problems. The future potential of these methods is such that they will soon become commonplace in our lives. Just as it is now impossible to think about getting things done without considering the role of the Internet, so will it soon be impossible to think about how to solve a large social problem without considering the role of open methods. Geoff Mulgan is Director of the Young Foundation and former Head of Policy in the Prime Minister's Office. Tom Steinberg is Director of mySociety and is currently a fellow at the Young Foundation. Omar Salem is a student at Oxford University and an intern at the Young Foundation.