Merger is a tool used by companies for the purpose of expanding their operations often aiming at an increase of their long term profitability. There are 15 different types of actions that a company can take when deciding to move forward using M&A. Usually mergers occur in a consensual (occurring by mutual consent) setting where executives from the target company help those from the purchaser in a due diligence process to ensure that the deal is beneficial to both parties. Acquisitions can also happen through a hostile takeover by purchasing the majority of outstanding shares of a company in the open market against the wishes of the target's board. In the United States, business laws vary from state to state whereby some companies have limited protection against hostile takeovers. One form of protection against a hostile takeover is the shareholder rights plan, otherwise known as the "poison pill".

Historically, mergers have often failed to add significantly to the value of the acquiring firm's shares (King, et al., 2004). Corporate mergers may be aimed at reducing market competition, cutting costs (for example, laying off employees, operating at a more technologically efficient scale, etc.), reducing taxes, removing management, "empire building" by the acquiring managers, or other purposes which may or may not be consistent with public policy or public welfare. Thus they can be heavily regulated, for example, in the U.S. requiring approval by both the Federal Trade Commission and the Department of Justice.

The U.S. began their regulation on mergers in 1890 with the implementation of the Sherman Act. It was meant to prevent any attempt to monopolize or to conspire to restrict trade.