We examine the emergence of InterContinental Transport (ICT) of air pollution on the agendas of the air quality and climate communities, and consider the potential for a new treaty on hemispheric air pollution. Intercontinental Transport is the flow of air pollutants from a source continent (e.g. North America) to a receptor continent (e.g. Europe). ICT of air pollutants occurs through two mechanisms: (1) episodic advection, and (2) by increasing the global background which enhances surface concentrations. We outline the current scientific evidence for ICT of aerosols and ozone, both of which contribute to air pollution and greenhouse warming. The growing body of scientific evidence for ICT suggests that a hemispheric scale treaty to reduce air pollutant concentrations may be appropriate to address climate and air quality concerns simultaneously. Such a treaty could pave the way for future climate agreements.