The world witnessed a change in the arrangement of international actors after the Second World War and the rise of international organizations in the international landscape. The International Maritime Organization (IMO) was one of these entities, acting as the UN specialized agency in maritime affairs. This study mainly aims at reviewing the regulatory role of the IMO, particularly the Port State Control (PSC) regime, by addressing its concept, as well as the legal basis and the control procedures. This mainly descriptive–inductive study describes and analyzes the legal bases of the PSC. Generally, IMO is identified with two types of functions: legislation and regulation. IMO’s regulatory function is reflected in two main tools, namely, the Audit Scheme of its Member States and Port State Control (PSC). With its supplementary nature, PSC is in fact an efficient maritime system for the safety and protection of the marine environment, encouraging states to watch for the safety of ships other than those flying their flags, especially those visiting their ports. This control system has led to an effective and efficient implementation of IMO rules and regulations.