This habilitation thesis comprises a compilation of publications that address central determinants of positive behavior across group boundaries, and that, taken together, significantly contribute to our knowledge about the processes that facilitate genuinely positive cross-group behavior. The thesis consists of four major parts. In a first part, I will provide a brief overview of traditional and emerging perspectives on positive cross-group behavior with special emphasis on research showing that forms of positive cross-group behaviors should be understood as a unique phenomenon that requires unique theoretical explanations (Publication 1). In a second and third part, I will introduce two research lines focusing on determinants of positive cross-group behavior in two different intergroup contexts – benign contexts of dyadic cross-group helping (Publications 2 to 6), and conflictual contexts characterized by direct or structural violence (Publications 7 to 10). Both lines address determinants that have not received much empirical attention in previous work. In a final part, I will discuss theoretical and practical implications of these two research lines, and outline two possible ways of integrating them by referring to two recent works (Publications 11 and 12). (Bei dieser Publikation handelt es sich um den Manteltext als Teil der kumulativen Habilitationsschrift.)