My thesis study is about the principles and case-law of ICSID in comparison with the dispute settlement mechanism of WTO. Under the WTO title, also mention briefly the process and function of NAFTA as an international tribunal. " WTO Dispute Settlement Body & Appellate Body " and " International Centre for Settlement of Investment Disputes(ICSID) " are the most important international tribunal ways and also the most common ways in practice. Most important differences between them about the parties of the disputes like IGO, state or companies and individuals. So, the WTO mechanism can be valid only between the states and IGOs but the ICSID mechanism can be valid only between the states and foreign investors. Occasionally these two instruments serve the same purpose which is about to solve the international disputes in international business law. But they are also totally different except that purpose. Also the NAFTA is about ICSID and not an different mechanism without ICSID. It is a subject of the ICSID. I will explain all of them with details and case law in that thesis study.