The availability of water in the Mediterranean in sufficient quantities and adequate quality represents a significant problem. This situation is particularly exacerbated on the islands of the Mediterranean. In this regard, MEDIS, an EU funded project, aims to give assistance in solving these problems and find solutions to this situation following a holistic, interdisciplinary approach, involving a major team of scientists, experts and stakeholders. For the realisation of the latter, scientific investigations of each island considered in MEDIS are required. Hence, the present volume includes a characterisation of each of the islands considered in MEDIS: Majorca, Corsica, Sicily, Crete and Cyprus comprising hydrological, agricultural and socio-economic data as well as water management schemes, laws and regulations.