In this paper, the basic concepts of port, island, and the general importance of maritime traffic between the mainland and islands are defined. Seaports are a key subsystem of the maritime and transport system and as such contribute to the development of various activities of each country. Constant investments are needed in their development so that they can accommodate as many people as possible, whether tourists or residents. Ports and maritime transport are particularly important for island states such as the Republic of Croatia, as numerous islands are connectes to the mainland exclusively by sea. Tourism demand, which is often higher on the islands than in the coastal area, also has a major impact on maritime traffic and the islands. Given that tourism plays a significant role in the Croatian economy, frequent maritime transport is one of the basic prerequisites for its smooth development. In addition to tourism, special attention is paid to nautical tourism, which is becoming more and more common on the Croatian islands. Nautical tourism ports attract an increasing number of high-paying visitors, whose consumption contributes to the island's development.