In a study of 124 dating couples, we tested a discrete systems model of the functions of two emotion systems in romantic relationships: love and anger/upset. This model posits that the operation of these systems reflects adaptations shaped by natural selection to solve different adaptive problems. Accordingly, we hypothesized that the love and anger/upset emotion systems would be largely independent in the classes of information they track in romantic relationships, in the psychological mechanisms that process that information, and in the resultant behavior generated. Consistent with the discrete systems model, and in contrast to a competing ‘crossover’ model, differences across relationships in feelings of love covaried with differences in strategic facilitation but not in strategic interference by partners. Similarly, differences in feelings of anger/upset during conflict covaried with differences in strategic interference but not strategic facilitation. In turn, feelings of love predicted commitment-promoting behavior but not partner-directed aggression, whereas levels of anger/upset predicted aggression but not commitment. As also predicted by our model, the love and anger/upset emotion systems converged to predict relationship satisfaction.