Vincent Mousseau

This book constitutes the conference proceedings of the 9th International Conference on Algorithmic Decision Theory, ADT 2026, held in Paris, France, during November 16-18, 2026.  The 39 full papers and 3 two-page abstracts presented were carefully selected from 75 submissions. The papers were organized in topical sections as follows: Elections and voting; fair division and resource allocation; games; and decision and preference modeling.