This "Research Commentary" explores the roles of theoretical and empirical work in the development of productive lines of research by elaborating on 3 main points. First, the dialectic between theory and empirical practice is highly productive for both: Theory is enriched by close attention to data, and one's understanding of empirical issues is deepened when one attends closely to theory. Second, an effective mechanism for making systematic progress is to focus on cases at the edge of one's (and the field's) collective theoretical understanding. Third, close observations of empirical phenomena often raise issues that have theoretical import and that give rise to new lines of work. These 3 points, and implications, are illustrated with examples from my research. (Contains 1 figure and 3 footnotes.)