Making use of official, international, and imperial archives alongside published sources, this chapter is a new international history of the late nineteenth-century expansion of Australian settler colonial jurisdiction, protection, and annexation of Pacific islands, focusing on Fiji and New Guinea – both of which were, at different times, integral to Australia’s federation project and certainly at the heart of Australian settlers’ cohering visions of empire. This chapter also shows how Australia’s expansion into the Pacific had major unrealized consequences for the legal bases of Britain’s international claims to colonial territories. It likewise demonstrates how Australian expansionists and their supportive publics, in participating in successful annexation schemes, created not only new colonial and imperial obligations for themselves, such as paying for colonial administration, but also international ones, such as protecting Indigenous populations in their territories – doctrines that required important revisions to their ideals of empire.