National territory and national borders are one of the main characteristics of every country today. For that reason, main focus of the international law is on the topics that will be shown in this paper. Questions that have to be elaborated to the smallest detail are mostly questions related to the national territory, sea as the part of the coastal state territory, marine premises where the coastal state has sovereignty or any other rights and national borders. Otherwise, it can lead to the dispute between the countries, which can be seen in some of the examples in this paper. The Republic of Croatia, as a relatively young country has also done a lot in the international relations regarding the national territory and national borders. In fact, there are also some disputes Croatia has with other countries, among which the Bay of Piran dispute stands out, also listed and described in this paper. Key words: national territory, sea as part of the coastal state territory, marine premises where the coastal state has sovereign or any other rights, national borders