Colonization is generally defined as a process by which states settle and dominate foreign lands or peoples. Thus, modern colonies are assumed to be outside Europe and the colonized non-European. This volume contends such definitions of the colony, the colonized, and colonization need to be fundamentally rethought in light of hundreds of ‘domestic colonies’ proposed and/or created by governments and civil society organizations initially within Europe in the nineteenth and first half of the twentieth centuries and then beyond. The three categories of domestic colonies in this book are labour colonies for the idle poor, farm colonies for the mentally ill, and disabled and utopian colonies for racial, religious, and political minorities. All of these domestic colonies were justified by an ideology of domestic colonialism characterized by three principles: segregation, agrarian labour, improvement, through which, in the case of labour and farm colonies, the ‘idle’, ‘irrational’, and/or custom-bound would be transformed into ‘industrious and rational’ citizens while creating revenues for the state to maintain such populations. Utopian colonies needed segregation from society so their members could find freedom, work the land, and challenge the prevailing norms of the society around them. Defended by some of the leading progressive thinkers of the period, including Alexis de Tocqueville, Abraham Lincoln, Peter Kropotkin, Robert Owen, Tommy Douglas, and Booker T. Washington, the turn inward to colony not only provides a new lens with which to understand the scope of colonization and colonialism in modern history but a critically important way to distinguish ‘the colonial’ from ‘the imperial’ in Western political theory and practice.