The North American region has been the site of sweeping economic, political, and social changes in the period since the negotiation of the North American Free Trade Agreement (NAFTA). In this introduction, Macdonald, Gabriel, and Ayres first provide a brief overview of some of the key concepts, notably transnational activism, scale, and scale shifting, that provide the analytic frames for considering cross-border mobilization in the region. They then move on to detail some key developments in the history of transnational activism in North America from the Canada–U.S. Free Trade Agreement (1988) to NAFTA and, finally, the United States–Mexico–Canada Agreement (USMCA), which resulted from Trump’s demand to renegotiate the agreement in 2019. The chapter concludes with a summary of each of the ten contributions to the volume.