This book constitutes the refereed proceedings of the 13th International Symposium on Algorithmic Game Theory, SAGT 2020, held in Augsburg, Germany, in September 2020.

The 21 full papers presented together with 3 abstract papers were carefully reviewed and selected from 53 submissions.

The papers are organized in topical sections named: auctions and mechanism design, congestion games and flows over time, markets and matchings, scheduling and games on graphs, and social choice and cooperative games.

* The conference was held virtually due to the COVID-19 pandemic.