An island's boundary - where it meets the sea - is self-evident and non-negotiable. But a land boundary is contestable: it can be changed and shifted to suit, reflecting power politics, the outcome of victor and vanquished in warfare, or negotiated compromise. There are today only ten inhabited islands where both these dynamics pan out. This text is the first to focus on the intriguing political economy of these rare, shared island spaces. It examines the fascination, and obsession, with islands as unitary geographies and polities; and explores the tensions in contemporary 'divided islands' - as in the case of formal and informal, legal and illegal 'border crossings' and practices - from both 'island studies' and 'international relations' perspectives.