The Seventh International Conference on Algorithmic Decision Theory has been held on November 3-5, 2021 in Toulouse, France as a hybrid conference. The program chairs have been David Rios Insua and Dimitris Fotakis and the local organizing committee consisted of Umberto Grandi, Sylvie Doutre, Laurent Perrussel, Pascale Zaraté, and Rachael Colley. A bit more than two third of the participants physically met onsite at the University of Toulouse 1 Capitole in a spacious auditorium while respecting all sanitary measures. The conference was preceded by a PhD day and thus allowed a large number of PhD students to participate at this event. The conference program included three invited talks by Edith Elkind, Christophe Labreuche, and Battista Biggio as well as twenty-seven regular talks. The talks covered topics such as preference elicitation and modeling, preference aggregation, computational social choice, voting, coalition formation, fair division and resource allocation, stable matchings, and participatory budgeting. The conference proceedings have been published as Volume 13023 of the Lecture Notes in Artificial Intelligence series.