Coalition formation games – preface

This special issue is devoted to coalition formation games, a central part of cooperative game theory with many real-world applications.Indeed, there are many situations in which individuals may choose to act as a group, or coalition, including social clubs, political parties, partnership formation, and legislative voting.The goal of coalition formation games is to partition a set of agents into coalitions, according to certain criteria, such as coalitional stability or maximization of social welfare.Especially interesting is a subclass of coalition formation games, hedonic games, which were first proposed by Drèze and Greenberg (1980) and later formalized by Banerjee et al. (2001) and Bogomolnaia and Jackson (2002).What makes hedonic games special within general coalition formation games is the requirement that each agent's utility must be entirely determined by the members of their own coalition.Preliminary versions of many of the papers in this special issue were presented in the special session on coalition formation games at the 17th International Symposium on Artificial Intelligence and Mathematics (ISAIM 2022), which in January 2022 (instead of taking place in Fort Lauderdale, USA, as in previous years) was done online via zoom sessions, because of the pandemic.However, this special issue is not a comprehensive proceedings of the ISAIM 2022 special session on coalition formation games, but rather consists of a selection of the best contributions presented at the conference, plus some carefully selected papers that fit the special issue theme.All papers accepted for publication here have run through the regular reviewing process of The Annals of Mathematics and Artificial Intelligence, with at least two reviewers for each submission and up to three rounds of reviews per paper.The reviews have been particularly detailed and helpful, and the editors are very grateful to all the reviewers for their time and invaluable effort to improve the submissions.This special issue covers a broad variety of topics related to coalition formation games, ranging from hedonic expertise games and hedonic games with common ranking property