Judith Butler's work has had a lasting impact on many debates in the social, cultural, and humanities fields for two decades. She is frequently present in literary sections as well as in political discussions. In 1991, her widely debated book "Gender Trouble" was published, presenting the provocative thesis that gender difference should be understood not biologically, but performatively. Today, Butler is considered one of the founders of Queer Theory and a philosopher who is attempting to formulate an ethics of vulnerability. This revised and expanded introduction places Butler's work in the context of contemporary discussions, addresses the controversial reception, and aids in understanding the complex arguments.