Our study examines the conditions under which firms enter into strategic alliances subsequent to knowledge spillovers. We propose that spillovers serve as signals of knowledge dependence and potential complementarity, encouraging alliance formation to enable better learning and limit appropriation. We posit that the likelihood of a knowledge alliance subsequent to a spillover is contingent on the specialization of each of the firms in the knowledge involved in the spillover. We also hypothesize that the effects of such specialization on knowledge alliance formation are moderated by technological ties and geographic distance between the dyad involved in the spillover. Our results demonstrate significance for the effects of specialization, supporting learning and appropriation motivations. Technological ties strengthen while geographic distance weakens the relationship between specialization and alliance formation.