This chapter argues the importance of national security issues in Australia–China relations, in particular as a factor in the decline of this relationship after 2015. The non-exclusive focus is on the prime ministership of Scott Morrison (2018–2022). From the Australian side, it takes up the revival of the “China threat” issue, Huawei, Chinese investment in Australia and Chinese influence in the South Pacific. On the Chinese side, it points out that, whereas Australia sees Hong Kong and Xinjiang as human rights issues, China sees them as matters of national security. Neither side has shown any sympathy for the national security concerns of the other. National security is asymmetrical. For Australia, China by itself is strong enough to be a national security concern, but for China, Australia is just part of the range of countries belonging to the American security alliance.