This article analyses Japan-China maritime relations with reference to economic, geopolitical and identity-politics factors, seeking to account for the shift from the high-point of cooperation in the East China Sea, around 2008, to the current, tense competitive bilateral dynamic centred there. A bitterly contested sovereignty dispute manifested in regular maritime confrontations around the Senkaku/Diaoyu islands is the most obvious indicator of deteriorating relations between Japan and China. Yet in spite of claims made about their economic and strategic significance, the islands are small, unpopulated and of limited material value. To account for why they have assumed such prominence as symbols of conflict between China and Japan, since September 2012, this article highlights the influence of wider geopolitical and ideational forces. It also considers the potential of Sino-Japanese maritime cooperation on such shared issues as shipping protection as a source of stability and normalcy in the bilateral relationship, and in a wider context, to what extent maritime commerce can continue to provide ballast against strategic rivalry and historical rancour between East Asia’s two largest economies.