While the world's oceans cover more than seventy percent of its surface, the sea has largely vanished as an object of enquiry in International Relations (IR), being treated either as a corollary of land or as time. Yet, the sea is the quintessential international space, and its importance to global politics has become all the more obvious in recent years. Drawing on interdisciplinary insights from IR, Historical Sociology, Blue Humanities and Critical Ocean Studies, The sea and International Relations breaks with this trend of oceanic amnesia, and kickstarts a theoretical, conceptual and empirical discussion about the sea and IR, by highlighting theoretical puzzles, analysing broad historical perspectives and addressing contemporary challenges. In bringing the sea back into IR, the book reconceptualises the canvas of international relations to include the oceans as a social, political, economic and military space which affects the workings of world politics.