The book is dedicated to the Ionian Sea, which is part of the Mediterranean. The encyclopedia contains about 600 articles on the hydrographic and geographic objects, hydrological features of the sea, biological resources, as well as administrative-territorial units of the Ionian countries. The most significant natural objects like islands, peninsulas, bays, rivers, mountains, their geographical peculiarities are briefly described as well as economy, culture and history, cities, ports, international agreements, research institutions, activities of outstanding scientists, researchers, travelers...