This article examines the common law approaches to the determination of the source of income with a focus on the Canadian source rules and with occasional references to those of other common law countries. The article discusses the source rules and treaty rules in general and the Canadian tax treatment of non-residents, including their business and employment income, capital gains and passive income. The article also looks at the relevance of the source rules to the foreign tax credit that may be available to residents having foreign-source income. The article concludes that there is a growing awareness that, in a global economy, if income is not taxed in the source country, it may not be taxed at all, which argues in favour of some shift from residence to source jurisdiction.