What motivates people to share what they know for the common good? Why do people edit pages in Wikipedia, contribute to the Zagat Guide, or participate in open-source software development when there is little or no (apparent) incentive to do so? Not only do traditional economic theories and models have little to say about the "economics of knowledge contribution," the issues are not even easy to talk about within existing theoretical frameworks. This grant will fund the work of economists Joshua Gans of the University of Toronto and Fiona Murray of the Massachusetts Institute of Technology as they seek to understand and explain the economics of why some uncompensated creative activities thrive for the benefit of society while others do not.