In an era in which accusations of “colonialism” are increasingly thrown around in political debate, it becomes necessary to define exactly what is meant by “colony.” As this article demonstrates, the heterogeneity and complexity of historical examples make it unexpectedly difficult to pin down exactly what this central term means and which historical territories should be described as “colonies.” The article considers three approaches to defining this key term: analytical, comparative, and historicist. While each has strengths and weaknesses, a case is made for greater historicist research in the future, as this approach is far less developed than the others.