The existence of an Australian ‘Monroe Doctrine’ articulating an Australian sphere of interest in the Pacific in the late-nineteenth and early-twentieth centuries is reasonably well known. Considerably less attention has been paid to the development of the idea that Antarctica and the Southern Ocean also constituted a uniquely Australian sphere of interest in the same period. This paper examines both the ways in which this idea was articulated and the efforts made to justify it through exploration, scientific research, and economic activities that eventually culminated in an assertion of Australian sovereignty. The paper seeks to broaden the geographical scope of what was understood as Australian in this period, and suggests that the origins of the idea that Australia had a unique interest in Antarctica highlights the significance of Australian expansionism in the nascent federal movement.