In September 2007, Canada and the United States signed the long-awaited fifth protocol to the 1980 Canada-United States tax treaty, concluding nearly ten years of negotiations. The changes made by the protocol are generally relieving in nature and were widely anticipated, but some of the changes are adverse to taxpayers and come as a surprise. Highlights of the protocol for businesses are the elimination of the withholding tax on cross-border non-participating interest payments; changes to the residence rules to provide or deny treaty benefits where hybrid entities are used; extension of the notion of "permanent establishment"; adoption of a taxpayer right to binding arbitration; and an update and extension of the scope of the limitation on benefits provision. This article discusses the principal changes made by the fifth protocol, focusing on matters relevant to cross-border business enterprises in light of the current issues and outstanding matters which remained after the substantial changes made by the protocols in 1995 and 1997, including withholding tax, hybrid entities, business profits, arbitration, corporate continuance, non-discrimination, limitation on benefits, migrants, and employees.