In this contribution to the Special Issue of European Taxation on treaty override the author outlines the complexity of the issue in the context of the rising importance of anti-avoidance, highlights the difference between treaty override and interpretation conflicts, provides a case study on treaty override in Canada, describes the OECD approach to treaty override in its 1989 Report on the topic and reflects on the concepts of Pacta Sunt Servanda and the "Object & Purpose of a Treaty".