Abstract: The ‘Indo-Pacific’ has emerged as the newest addition to the lexicon of Asian regionalism. Conceived of as the conjunction of the Pacific and Indian Oceans, it reflects the belief that maritime linkages require extending Asian regionalism westwards to include countries on the Indian Ocean rim. It also competes with the longstanding ‘Asia-Pacific’ conceptualisation of the region, and four governments—Australia, India, Japan and the USA—have adopted it into their foreign policies. Much of the debate on the Indo-Pacific focuses on how it institutionally ‘rescales’ Asian regionalism through the incorporation of Indian Ocean states. This article considers the functional rescaling that attends this process: namely, what kind of regionalism is implied by the Indo-Pacific concept? It argues that the Indo-Pacific is a security-focused regional project, reflecting the desire of its proponents to form a quadrilateral bloc to resist China’s growing maritime assertiveness. This security region is radically different from the Asia-Pacific concept, where regionalism was primarily driven by economic integration and cooperation. The Indo-Pacific thus marks a more contested period in Asia’s international politics, where the functional purpose of regional cooperation is being reoriented from economic- to security-focused agendas.