This thesis analyses the operation of the general anti-avoidance statutory rules and doctrines from the perspective of their compliance with the principle of the Rule of Law. The main question that it will try to answer is what characteristics these rules and doctrines should have in order to control tax avoidance in a manner that is compatible with the principle of the Rule of Law. For this purpose, this thesis will take the following approach. First, it will explain the causes of tax avoidance and why the legal mechanisms directed to attack it are in tension with the principle of the Rule of Law. Second, it will propose a relatively straightforward concept of the Rule of Law in order to test the different judicial and statutory anti-avoidance mechanisms. Third, it will analyze the consistency of those mechanisms with the proposed concept of the Rule of Law. And finally, it will explain what characteristics a general anti-avoidance model should have to comply with the principle of the Rule of Law and it will show why a statutory model of general anti-avoidance rules is required for that purpose.General anti-avoidance statutory rules and judicial doctrines are designed to control any transaction that escapes taxation and is incompatible with the tax policies implemented by the relevant tax statutes. For this purpose, these rules and doctrines define what counts as an avoidance transaction in extremely wide and generic terms. In consequence, the application of these provisions to concrete cases demands important interpretative efforts and, for the same reason, creates significant space for judicial and administrative discretion.