This review essay provides a comprehensive roadmap of the international law of peace, which has not been so presented in the International Law-International Relations literature before. In Part 1 we review peace law as such, that is, where it is simply and directly mandated in international law. In the second of the two parts, we depict international law that does not mandate peace, but requires behavior that indirectly results in peace. In both parts the three sources of international law, treaty, custom or principles are identified, along with soft law, which is incipient, but non-binding. Laws of peace per se include all the United Nations Charter provisions (treaty and customary) related to peace and peaceful conditions, jus ad bellum (custom) and the law against aggression (treaty), the 1970 Declaration on Friendly Relations Among States (custom and principle) and the Human Right to Peace (custom, soft law). Indirect effects of international laws and conditions on peace include the Vienna Convention on the Law of Treaties (treaty), all international treaty regimes (treaty), expanding authority of international actors and institutions in creating and interpreting international law (custom), humanitarian and human rights law (treaty), and the Responsibility to Protect norm (soft law). The review takes a legal approach. Development of peace law is placed in the history of international law and within the progressive development of international law today. All peace law per se in Part 1 is found to be legalized and binding except the Human Right to Peace which is legalized but non-binding so far. The review identifies how peace is the ultimate purpose of all international law.