Tax law is often addressed by legal academics from a strictly substantive point of view, emphasizing issues related to law-making power and its limits, neglecting adjective questions connected to the procedure. In this article I argue that administrative and judicial procedures shall not be seen as peripherical or mere technical questions, and are so noteworthy as any other legal subject. Moreover, they shall be designed considering the essential values and principles of the legal system, namely the Rule of law (a meta-principle) and cooperation (the keystone of an ethical, fair and developed tax system).