The rights and duties of flag States go hand in hand under the UNCLOS legal framework. A State bears the right to grant a ship its nationality and is entitled to exercise exclusive jurisdiction over the ship. At the same time, a flag State has the obligation to effectively exercise its jurisdiction and control over the ship sailing under its flag. While the provisions relating to flag States’ rights and obligations are found in Part VII UNCLOS entitled ‘High seas’, their application apply to wherever the ship may find itself. Given the omnipresence of ships at seas, clarity and certainty regarding flag States’ rights and obligations is crucial for the effective implementation of UNCLOS, as well as for ensuring delicate balance between the rights and obligations of coastal States and of flag States upon which UNCLOS hinges. This chapter examines the decisions of UNCLOS tribunals relating to flag States’ rights and obligations, in order to examine whether and to what extent UNCLOS tribunals have contributed to the clarification and development of the relevant rules pertaining to flag States.