This article examines the history of antitrust policy on mergers of ATM networks. The author notes that a series of ATM network mergers have resulted in virtual monopolies of ATM systems within large regions of the country. He interprets the actions of the antitrust authorities (including the Federal Reserve in its role of approving acquisitions by bank holding companies) as reflecting the view that regional ATM networks have characteristics of natural monopolies. He challenges the view that regional ATM networks are natural monopolies and argues for the benefits of preserving network competition. He cites cases of vigorous competition between ATM networks that ceased when networks merged. He ends his article with a warning that the policy of permitting the formation of ATM network monopolies over large regions will require involvement of government agents (including the Federal Reserve).