This paper analyzes the impact of managerial horizon on mergers and acquisitions activity. The main predication is that acquiring firms managed by short-horizon executives have higher abnormal returns at acquisition announcements, less likelihood of using equity to pay for the transactions, and inferior postmerger stock performance in the long run. I construct two proxies for managerial horizon based on the CEO's career concern and compensation scheme, and provide empirical evidence supporting the above prediction. Moreover, I also demonstrate that long-horizon managers are more likely to initiate acquisitions in response to high stock market valuation.