Supreme Court justices employ law clerks to help them perform their duties. We study whether these clerks influence how justices vote in the cases they hear. We exploit the timing of the clerkship hiring process to link variation in clerk ideology to variation in judicial voting. To measure clerk ideology, we match clerks to the universe of disclosed political donations. We find that clerks influence judicial voting, especially in cases that are high-profile, legally significant, or when justices are more evenly divided. We interpret these results to suggest that clerk influence occurs through persuasion rather than delegation of decision-making authority.