In recent years, companies have formed complex alliances and operating agreements that allow the sharing of information among participants in specific supply chains. Because many of the companies involved in these arrangements are large businesses with a wide range of operations, they often find themselves competing with another company in one line of business while supplying, partnering, buying from that same company in other lines of business. The use of Internet technologies has enabled these companies to share information in highly selective and closely monitored ways, which is important when the other company might simultaneously be a competitor and a partner, for example. In the US, government regulators considering antitrust action or reviewing proposed mergers are required to evaluate these relationships and information flows among the parties. This paper examines the issues that arise from information sharing in today supply chain relationships.