On December 12-13 2012, CAIDA and the Massachusetts Institute of Technology (MIT) hosted the (invitation-only) 3rd interdisciplinary Workshop on Internet Economics (WIE) at the University of California’s San Diego Supercomputer Center. The goal of this workshop series is to provide a forum for researchers, commercial Internet facilities and service providers, technologists, economists, theorists, policy makers, and other stakeholders to empirically inform current and emerging regulatory and policy debates. The theme for this year’s workshop was ”Definitions and Data”. This report describes the discussions and presents relevant open research questions identified by participants.