Data from a longitudinal sample of dating couples (some of whom married) were analyzed to test the aspect of Waller's (1938) principle of least interest that states that unequal emotional involvement between romantic partners has implications for relationship quality and stability. Both members of the couples were asked multiple times over several years which partner, if either, was more emotionally involved. Perceptions of unequal emotional involvement were common and tended to remain stable over time. Less emotionally involved partners perceived themselves as having more control over the continuation of their relationships. Equal emotional involvement was associated with greater relationship satisfaction and stability. Concurrent and retrospective perceptions of relative emotional involvement were associated with several aspects of relationship breakup within the subsample of those who broke up during the study. Perceptions of emotional involvement have many implications for dating couples, including being linked to relationship satisfaction and other outcomes. (Contains 3 tables and 2 notes.)