Coordination costs among a firm’s shareholders have an important impact on the market for corporate control. I use two measures, one based on the geographic distance among institutional shareholders and the other based on the correlation in their portfolio allocation decisions, to proxy for coordination costs. I find that target firms with low shareholder coordination costs experience significantly higher abnormal returns around the takeover announcement. In a similar vein, acquirer firms with low shareholder coordination costs are associated with higher acquisition announcement returns. These effects are particularly pronounced after the 1992 proxy reform that relaxes the restrictions on communication and coordination among shareholders. These findings suggest that the ease of coordination among shareholders plays an important role in the market for corporate control by raising the bargaining power of target shareholders and enhancing the monitoring role of both target and acquirer shareholders.