Proceedings of the 13th Conference on Theoretical Aspects of Rationality and Knowledge (TARK-2011), Groningen, The Netherlands, July 12-14, 2011

We have quite a reason to celebrate: the first TARK (Theoretical Aspects of Rationality and Knowledge) conference took place 25 years ago. In the meantime a number of related developments took place in computer science, such as the rise of multi-agent systems, algorithmic game theory and computational social choice. This happened because the barriers between mathematical logic, computer science and economics got definitely broken. It is fair to say that the series of the TARK conferences played a large role in this change. Its multidisciplinary character, focusing on the intersection of the above three disciplines, is not anymore novel and it became an accepted view of a broad and fascinating research area. The present volume consists of the proceedings of the 13th TARK conference that took place in Groningen, the Netherlands, July 12--14, 2011. The programme consisted of 18 papers selected out of 65 submissions. Additionally 9 papers were accepted as posters and were also published in the proceedings. The programme also featured two invited talks, by Johan van Benthem and Yossi Feinberg, and two invited tutorials, by Ithzak Gilboa and Larry Moss.