Using millions of siblings in the U.S., we detail three findings that quantify whether siblings influence one another to vote in national elections. First, and descriptively, younger siblings are 10 percentage points (50 percent) more likely to vote in their first eligible election when their older sibling votes in a prior election. Second, roughly one-third of this is caused by the older sibling voting, as determined by age-of-voting-eligibility thresholds in a regression discontinuity design. Third, the causal impact of a sibling voting runs in the other direction as well---younger siblings increase the probability of their older siblings voting in their early 20's by 14 percent. These results demonstrate the influence and importance of family and peers in creating an engaged citizenry and underscore that across a wide array of policy domains, conventional impact evaluations do not fully account for all of policies' impacts.