In this paper, we assess the drivers of, and prospects for, further security cooperation in the Australia–Japan bilateral relationship. We argue that while balance of threat and capability gaps may restrain the pace of deepening Australian-Japan security relations, these gaps are diminishing and are, in any case, secondary to the specific shared interests we posit as the primary drivers of Australia–Japan security cooperation. These specific interests, however, are shaped not only by a commitment in both countries to liberal-based principles and freedoms at home and in inter-state relations, but also by a common awareness of the importance of continued US primacy to the ongoing maintenance of those interests. Thus, in the absence of any fundamental change in how Australia and Japan understand their respective interests and the US role in the region, Donald Trump's recent and unexpected election as US president notwithstanding, we conclude that the case for further security cooperation – via additional cross-bracing of their respective US alliance relationships – will almost certainly remain compelling for both countries.