Although significant scholarship has been devoted to the study of corporate political activity, contradictory messages emerge regarding its impact on public policy outcomes and firm performance. Using meta-analytic methods on a US-only sample of 93 studies, working papers, and books, we try to disentangle two mechanisms that explain why corporate political activity is not always beneficial to firms: (1) the uncertainty about the public policy process itself, that is, can firms get the policies they want through corporate political activity? and (2) the uncertainty about the policies’ impact on the firm, that is, whether firms effectively anticipate the implications of policies for their performance. Our results support the idea that these types of uncertainty play an important role in explaining the intermediary dynamics of corporate political activity. We find that in the United States, corporate political activity only weakly impacts public policy and at best has a (direct) weak effect on corporate outcomes.