This thesis consists of five chapters. Chapter 1 is the preliminaries. Chapter 2 to chapter 4 are the three main chapters of this thesis, which cover the U.S. market. Chapter 5 is the discussion. Chapter 1 is the preliminaries. It introduces the setting and motivations for the three topics covered in this thesis. Chapter 2 investigates how the removal of short selling constraints affects a firm’s mergers and acquisition (M&A) using Regulation SHO’s pilot program as a natural experiment. The SEC in the U.S. randomly selected stocks in the Russell 3000 index into the pilot group for which various short sale constraints were removed. I find that during the pilot program, firms in the pilot group significantly reduce their value-destroying M&A ...