This essay explores the nature and status of two common law principles concerned with the protection of human rights: the 'principle of legality' (legislation can only abrogate certain common law rights expressly or by necessary implication) and the 'treaty presumption' (legislation is to be interpreted in accordance with the Crown's obligations under international treaties). The survey of these principles covers the law in England and Wales, Australia, and New Zealand. In each of these countries, human rights legislation applies, which contains an interpretive rule similar to the common law principles. This essay demonstrates that, despite such statutory rules, the common law principles continue to be relevant to varying degrees in the different countries under consideration. In so doing, a useful summary of the issues surrounding the application of the principles is provided, including consideration of whether ambiguity is required to be found before the principles can come into play and the sort of statutory language that is required to rebut the presumptions that they create. The essay concludes by raising the possibility that Australia and New Zealand are departing from English law in this area. © The Author 2013. Published by Oxford University Press.