Abstract This paper evaluates current antitrust policy in light of our current understanding of how transaction costs influence the ability of firms and consumers to deal with market power. The paper shows how the failure to consider transaction costs can lead to erroneous policy decisions. Many models employed today make simplifying assumptions about transaction costs that can lead to biased results in analyzing vertical and horizontal issues. The increased ability to monitor the effect of promotional behavior should cause us to reexamine whether free riding justifications, previously accepted as justifications for various vertical restrictions, still hold. Nash bargaining and Nash-in-Nash models raise concerns about the simplified assumptions assumed in which supposedly high transaction costs restrict the choice and form of the assumed competitive alternatives. The increasing importance of two-sided markets together with an understanding of transaction costs is needed to understand antitrust conduct in those markets. The recent Amex case is likely to lead to confused litigation in these types of markets. Finally, the establishment of property rights for a consumer to his or her data could fail to remedy antitrust concerns that certain dominant firms are immune to competition because consumers do not own their data unless that property right is limited so that consumers cannot exclusively sell their data to one firm.