A highly debated question that engages paleontologists, zoogeographers, and zoologists is how terrestrial mammals colonize islands. The question’s oversimplification and the subjective and partial responses to it have led to reductionist models. Insular faunas and fossil assemblages result from a complex interaction of geological, biological (in a broad sense), climatic, eustatic, taphonomic, and historical processes. Insular assemblages and their accompanying variables should be investigated on a case-by-case basis. In this article, we discuss not only common misconceptions and their potential origins but also the key issues that should be addressed when dealing with the colonization of islands by land mammals. We call for the implementation of multi- and interdisciplinary research programs and teamwork, involving paleontological, geological, and stratigraphic information; climatological factors; sea-level evolution; sampling and analytical biases; ecological, physiological, taphonomic, and environmental factors; behavioral characters and ecological preferences; genetics; phylogeography; densities of colonizing populations; and historical reports of human-mediated faunal introductions.