This book constitutes the thoroughly refereed proceedings of the 12th International Conference on Web and Internet Economics, WINE 2016, held in Montreal, QC, Canada, in December 2016. The 35 regular papers presented together with 3 invited talks were carefully reviewed and selected from 88 submissions. The Conference on Web and Internet Economics (WINE) is an interdisciplinary forum for the exchange of ideas and results on incentives and computation arising from the following fields: Theoretical Computer Science, Artificial Intelligence, and Microeconomics.