Nineteenth-century mutualism is not seldomly depicted as a sympathetic but inherently flawed (upper) working-class movement that by necessity was crowded out by state action. In contrast, this thesis traces and compares mutual sickness insurance traditions in order to understand better why three countries with strong mutualist traditions had developed into widely different welfare states by the mid-1970s. By comparing mutual sickness insurance traditions in Denmark, the Netherlands, and the United Kingdom, this dissertation also connects theoretical assumptions about mutualism and the emergence of welfare states with national historiographies on mutual insurance and social policy. Section 1 traces the historical origins of mutual sickness insurers and situates their operation in the mixed economy of welfare in the period 1870-1920. It explores why Danish and Dutch mutuals specialized in health insurance, whereas in the UK especially the so-called affiliated orders increasingly applied actuarial knowledge to guarantee cash payments during ill-health. Finally, the first section explains why Danish mutuals managed to insure larger sections of the working classes both in rural and urban areas than their Dutch and British counterparts – an observation that sits uneasily with historiographical depictions of nineteenth-century mutualism as an urban phenomenon that mostly attracted (male) waged workers in industrialized areas. Section 2 traces the mutuals within the wider mixed economy of welfare in the interwar period and from the outbreak of the Second World War until the mid-1970s, with a special focus on the consequences of war and industrial depression on the operation of the insurers. In so doing, it finds that the coordination of health insurance with other social risks (e.g. disability, sick pay, unemployment) in the early stage of social reform (i.e. 1870-1920) had crucial consequences for coverage rates in the interwar period, and for the legitimacy of national arrangements after the Second World War.