An island country, island state, or island nation is a country whose primary territory consists of one or more islands or parts of islands. Approximately 25% of all independent countries are island countries. Island countries are historically more stable than many continental states but are vulnerable to conquest by naval superpowers.

There are great variations between island country economies: they may rely mainly on extractive industries, such as mining, fishing and agriculture, and/or on services such as transit hubs, tourism, and financial services. Many islands have low-lying geographies and their economies and population centers develop along coast plains and ports; such states may be vulnerable to the effects of climate change, especially sea level rise.

Remote or significant islands and archipelagos that are not themselves sovereign are often known as dependencies or overseas territories.