This research examines the incentives and constraints that shape user-led creativity in online platforms. Inspired by theory on private-collective innovation, my work seeks to identify the conditions under which creators will freely offer their work to be modified by others, or in turn will incorporate freely available inputs into their own creative production. I am further interested in how these dynamics differ between commercial platforms and commons-based platforms such as the Wikimedia Commons. My presentation draws primarily on two recent projects: a study of the risks and rewards of engaging in remix on the crowdfunding platform Kickstarter, and a study to estimate the value of imagery contained in the Wikimedia Commons. A key challenge of this work is developing methodologies to allow statistical analysis of subjective qualities of creativity. I hope to discuss some of those challenges and the strategies I have used to address them in this talk.