This paper examines the carbon impact of online retailing and compares it with that of conventional retailing. It discusses the effect of varying the scope of the calculation, the system boundaries and the underlying assumptions. While most of the carbon emissions come from the last-mile delivery, this is also the activity whose carbon intensity is most sensitive to assumptions made about consumer behavior. On the basis of an extensive literature review, the paper also explores the carbon impacts of the upstream supply chain, energy use in information and communication technology and several aspects of travel behavior. This should help researchers to make wider and more realistic assessments of the environmental impact of online retailing. On the basis of these assessments, one can test the conditions under which online shopping is likely to have a lower carbon footprint.