The term ‘coastal State’ is not defined under UNCLOS despite being one of the most frequently used terms. In the EEZ, UNCLOS confers upon coastal States both exclusive sovereign rights and jurisdiction over natural resources and jurisdiction in relation to artificial islands, installations and structure, marine scientific research and environmental protection. However, the scope of these rights and obligations is not always clearly set out in the relevant provisions, requiring further clarification and elaboration. Moreover, due to the new scope of power given to coastal States in the EEZ, the question has arisen as to how coastal States’ rights and obligations in this new maritime zone, as well as coastal States’ rights and obligations in the territorial sea and the high seas, interact with historic claims arising prior to the entry into force of UNCLOS. This chapter analyses the decisions rendered by UNCLOS tribunals addressing the abovementioned issues and assesses the extent to which they have contributed to clarifying relevant rules relating to coastal States’ rights and obligations under the law of the sea.