The subject matter of this thesis is freedom of navigation on the High Seas, with particular reference regarding convenient flags, namely flags of convenience. The concept of the freedom of the Seas, together with notion that it benefits us all and therefore, in the light of that universal character, it belongs to all of mankind, originates from ancient times and the works of renowned Roman jurists. Similarly, the concept of freedom of navigation can be considered as one of the greatest attainments of the development of the international law of the sea and likewise, one of the most complete manifestations of the freedom of the Seas, as well as its most significant component. Freedoms of the High Seas, within the context of one of the most relevant international legal instrument, ie the 1982 United Nations Convention on the Law of the Sea will be analyzed in this thesis. In so doing, particular focus is on the importance of the restrictions of the aforementioned freedoms, that is best outlined in the scope of duties imposed onto states either through Convention itself, or other international treaties and organizations. Considering that every constraint of certain freedom also entails increase or broadening of other freedoms, all of the forgoing is furthermore viewed through the powers given to states, respectively jurisdiction of operations on the High Seas. Those operations certainly qualify as an exception, however, sometimes essential for the benefit of the whole international community, revived through an universality principle. Moreover, the final chapter of this thesis accentuates the significance of the issue concerning flags of convenience. Notwithstanding the motives of their utilization and taking into account multitude of tax reductions and benefits they provide, as well as their frequent use in less developed countries, the damages they inflict and the consequences incurred are extensive and longlasting. Therefore, the amount of controversy they generate is not surprising at all. The latter is best illustrated through the international legal regulation and its versatile endeavours and efforts regarding combating and prevention of flags of convenience, as well as the open registry ships related to them. Nevertheless, the most effective measures lie within the national legislation of states.