Invasive species pose major threats to island ecosystems, often disrupting ecological dynamics and driving the decline or extirpation of native species. Their introduction typically brings novel functional groups to which island biotas are particularly vulnerable, due to their low diversity and unique ecological traits. Isla de los Estados, a protected area, was originally inhabited by only two native terrestrial mammal species prior to European arrival. Although it currently lacks permanent human settlements, the island continues to face pressure from several exotic mammal species historically introduced by sealers, whalers, sailors, and early ranching efforts. This chapter reviews the history of non-native mammal introductions and establishment on the island, alongside documented impacts from similar invasions globally. Drawing on nearly a decade of fieldwork, including vegetation surveys, diet studies, camera trapping, and exclusion experiments, we summarize the current understanding of introduced mammal population and their ecological impacts on native species and habitats. We also explore the potential for interactions among invasive species to amplify their effects across trophic levels and ecosystems. Finally, we identify key research needs and propose future steps for managing invasive species and restoring native ecosystems on this unique sub-Antarctic Island.