We exploit seating rules in the European Parliament to identify peer effects in legislative voting. Sitting adjacently leads to a 7 percent reduction in the overall likelihood that two members of the European Parliament (MEPs) from the same party differ in their vote. Peer effects are markedly stronger among pairs of women, MEP pairs from the same country, and in close votes. Using variation in seating across the parliament's two venues (Brussels and Strasbourg), we show that peer effects are persistent: MEPs who have sat together in the past disagree less even when they are not seated adjacently.