This chapter reports data from a longitudinal exploratory case study of two strategic alliances with the aim of achieving a better understanding of interpartner dynamics. Combining insights from the response strategy perspective and interpersonal theory, we propose that response strategies are organized along the circumference of a circle in a two-dimensional space. In such a circumplex structure, the complementarity principle, explaining how partners respond to each other, is composed of two rules: the rule of reciprocity and the rule of correspondence. The objective of this chapter is to explain when and why alliance partners follow or deviate from these rules. Evidence from the two strategic alliances indicates that the response behaviors derived from interpersonal theory can be identified at the interorganizational level in a strategic alliance. Moreover, partners often use a complementary behavior. The findings, however, also provide insights into three mechanisms that trigger partners to use noncomplementary behavior. This study provides a fine-grained explanation for alliance partner intcraction and offers a tentative first step in building an integrative model of interpartner dynamics in strategic alliances.