This study examines key requirements & components of a Canada-United States cross-border cap & trade program for sulphur dioxide (SO2) & nitrogen oxides (NOx) emissions. Section A explains the air quality information relevant to the Canada-US transboundary region, including air quality problems shared by both countries, sources & geographic distribution of precursor emissions, and shared source regions. Section B analyzes the legal framework relevant to a cross-border emissions cap & trading program and describes the legal authority whereby Canada could establish such a regime. Section C examines which industrial sectors are well matched to a cross-border emissions cap & trading program. Section D discussions emissions monitoring & reporting in the two countries and highlights the need for harmonization of the two regimes under a cap & trading program. Section E covers allowances, or the tradable units of a program. It describes allowances & their use, including areas of jurisdictional flexibility such as allowance allocation methods. Section F discusses principles for designing an electronic registry, its components, and centralization of a registry for tracking allowances & emissions. Section G addresses the key questions of compliance & enforcement considerations for a cross-border emissions cap & trading program. Section H uses emission & air quality models to demonstrate the feasibility of analyzing illustrative emission management scenarios.