At first glance, administrative law in Canada, where courts regularly defer to administrative decision-makers’ interpretations of law and judicial review of administrative action is organised around the concept of reasonableness, is very different to administrative law in England, where courts do not defer to administrative interpretations of law and prefer to conceive of the justification for judicial oversight of administrative action in terms of grounds of review and jurisdictional error. One might think, based on this first glance, that the differences must be attributable to deep-seated disagreement about the nature of judicial power and the appropriate allocation of interpretive authority between the branches of government. One might even suspect that such disagreement must rest on long-settled historical foundations. I will argue, however, that the difference between Canadian and English administrative law is best explained by relatively recent accidents of history. Indeed, I will suggest, a prolonged period of divergence may be coming to an end, with the Transatlantic rise of reasonableness review ushering in a new era of convergence. I will develop this argument by tracing the pattern of divergence and convergence in Canadian and English administrative law from the 1970s to the present day. From the common starting point identified in Part I, the two jurisdictions diverged dramatically between the 1970s and 2000s, as I will explain in Part II. Since then, the administrative law of the two jurisdiction has converged to some extent, as outlined in Part III. One of the implications of my argument is, as I discuss in Part IV, is that further convergence in the future is possible. Moreover, a corollary of this argument is that there is room for fruitful comparisons of English and Canadian administrative law. My message, to those who fear – for whatever reason – that “there be dragons”, is that they can safely venture forward in an Anglo-Canadian comparative administrative law endeavour. A reader interested in undertaking comparative analysis might well conclude that the nature of judicial power, the appropriate allocation of interpretive authority and long-settled historical foundations are substantially similar in both jurisdictions.