While the use of the term “Indo-Pacific” is relatively new, debates about its use echo longstanding arguments about how the region should be defined: who is in, who is out, and on what terms. Under two successive U.S. administrations, the term Indo-Pacific has become the accepted way that the United States refers to the broad geographic region stretching from the western Indian Ocean through Southeast Asia and into Northeast Asia and the Pacific. However, adoption of the concept in Southeast Asia remains mixed. At Indonesia’s urging, ASEAN in 2019 adopted its “Outlook on the Indo-Pacific” (AOIP), and Indonesia itself readily uses the term. This article sets out the key elements of both the U.S. approach to the Indo-Pacific and Southeast Asian approaches to the Indo-Pacific, primarily focusing on Indonesia’s perspective, reflected in the AOIP. It identifies common concerns, especially an emphasis on maritime cooperation, as the driver of convergence, as well as several areas of divergence. Among these divergences are questions about the value of cooperation as a driver rather than the product of strategic trust; and the relative importance of “inclusive” versus “exclusive” or “minilateral” cooperative mechanisms. In large part, these divergences reflect underlying disagreements between the United States and Southeast Asian countries about how to engage China.