After a brief overview of the general international rules concerning treaties, this Chapter explores how treaties rely in different measures on some form of parliamentary approval (the institutional strategy), corresponding to the classic precepts of the separation of powers allocating the final (if not exclusive) say in law-making to a responsible and representative legislative branch. Thus the primary tension in the separation of powers regarding treaties obtains between the legislature and the executive, specifically the powers of the executive to make and import rules. While the implementation of international law through treaty provisions offers the courts an easy solution to separation of power concerns by virtue of the institutional strategy, the imbalance it brings to the classic equilibrium between legislature and executive ultimately plays itself out in the courts as a choice between the reflexive and presumptive strategies.