Emerging online innovation platforms have enabled large groups of people to collaborate and generate ideas together in ways that were not possible before. However, these platforms also introduce new challenges in finding inspiration from a large number of ideas, and coordinating the collective effort. In my dissertation, I address the challenges of large scale idea generation platforms by developing methods and systems for helping people make effective use of each other's ideas, and for orchestrating collective effort to reduce redundancy and increase the quality and breadth of generated ideas.