This volume compiles the latest research and theory on close relationships in the twenty-first century from multi-disciplinary and international perspectives with the intent of taking stock of the cultural, political, and legal changes that have shaped the relationship landscape. Some of the important shifts that are captured are the rise of singlehood, online dating, and cohabitation, the new importance of social media, marriage equality, and changes in gender norms. New ways of forming families and unions via adoption, assisted reproduction, and remarriage are also covered, as well as coupling across cultural, racial, religious, and national lines.