Recent public concerns and publicity about the extent of tax avoidance by some of the largest and most respected transnational corporations (TNCs) have prompted numerous parliamentary inquiries and intergovernmental initiatives. Among the questions raised during hearings in the UK House of Lords in 2013 were whether such avoidance could be more effectively prevented either by a reduction in the complexity of the rules, or by a more aggressive interpretation of those rules by tax authorities. These questions raised issues concerning the complexity and interpretation of law, which received interestingly different responses from the academics to whom they were posed, and they merit closer examination, which is the aim of this paper. It begins by discussing some types of complexity, and then considers how these are rooted in the indeterminacy of legal language, and the sociology and politics of the interpretive communities concerned. The main part applies this analysis to the historical development of international tax rules, seen in the context of these current pressures and initiatives for reform of international corporate taxation.