This book constitutes the refereed proceedings of the 17th International Conference on Web and Internet Economics, WINE 2021, which was held online during December 14-17, 2021. The conference was originally planned to take place in Potsdam, Germany, but changed to a virtual event due to the COVID-19 pandemic. The 41 full papers presented in this volume were carefully reviewed and selected from 146 submissions. They were organized in topical sections as follows: mechanism design and pricing; matching, markets and equilibria; learning, fairness, privacy and behavioral models; social choice and cryptocurrencies.