Abstract: Merger and acquisition deals are governed by merger clauses which are negotiated between the bidder and target in order to communicate deal terms, specify risk sharing between the parties, and describe dispute management provisions in case of litigation. In a large sample of manually collected U.S. deal contracts involving publicly traded bidders and targets, we construct merger clauses indices based on legal scholars’ ex-ante prediction and examine the relationship between announcement returns and different types of merger clauses. We find that bidder protective clauses correlate with higher bidder returns while target protective clauses and pro-competition clauses correlate with higher target returns. We also find that bidder and target protective indices have larger impacts on announcement abnormal returns for “bad” deals than for “good” deals. Finally, we find that the inclusion of more bidder protective clauses leads to lower deal completion rates while the inclusion of more target protective clauses and pro-competition clauses has no impact on deal completion rates. These results are consistent with the expert lawyer/efficient contracting view of Cain, Macias, and Davidoff Solomon (2014), and Coates (2016), and against merger contracts as boilerplate agreements.