Signing statements have become an important device that both protects and enhances presidential power by signaling how legislation is to be implemented, offering a mechanism of electoral reward, and protecting presidential prerogatives. We offer a first cut at explaining signing statements by applying William Howell's theory of unilateral action. The evidence shows that presidents use signing statements under conditions of gridlock, such as divided government, which erode their influence in Congress. The findings also suggest a strategic element to signing statement behavior. Presidents issue significantly more signing statements on major legislation when the policy and political stakes are greatest. The results provide insight into the theory of unilateral action and demonstrate how signing statements complement rather than contradict the Richard Neustadt view of power.