Abstract: Maritime security challenges in the Asia–Pacific are increasingly at the forefront of both academic and policy concerns, both inside and outside of the region. The intense geostrategic competition in the South China Sea partially explains the growing interest, but the attention goes deeper than that. The rise of new maritime powers in the Pacific, as well as increasing concerns over a clash between the United States and China, underscore the burgeoning importance of the maritime Asia–Pacific. While much of the research on Asian–Pacific maritime security focuses heavily on the experiences and strategies of the major powers, it is also important to understand the perspectives and policies of other actors in the region. This article focuses specifically on the maritime security perceptions of Australia and New Zealand: Using interviews with and publications by trans‐Tasman experts, I sketch the dominant threats perceived by the countries in their maritime environments. Important policy conclusions can be drawn from this analysis of perceptions of maritime security challenges Down Under. Perhaps the timeliest policy insight is that as the United States considers whether or not to confront China over its behavior in the South China Sea, it is unlikely to receive full support from all of its mates in the region. The paper also argues that understanding key maritime security challenges – from the pragmatic to great powers relations – requires an openness to understanding how maritime security threat perceptions are constructed by identity and other ideational factors.