This dissertation, organized both chronologically and thematically, explores the long term development of the Swiss health insurance system, and takes as its specific object of investigation the providers of insurance services, and in particular the mutual sickness funds. Chapter 1 studies the emergence in the 19th century of an “actuarial science of sickness”, and examines the reaction of the mutualists, in particular of Western Switzerland, to the pressure that the new actuarial paradigm exerted on their organizations, in a context characterized by the growth of the Federal State. Chapter 2 analyzes the development, from the early 1920s onwards, and through the case of the Société vaudoise de secours mutuels, of medical care insurance. This new insurance modality profoundly transformed the economic activity of the mutuals, and contributed to give to the notion of health insurance the meaning that we nowadays ascribe to it. The diffusion of this innovation led in the 1930s to a rapid growth of the costs, which itself gave rise to the first reforms intended to control medical inflation. Finally, chapter 3 studies the period going from the mid-1930s to 1970, characterized by the penetration in the branch of a new actor: life insurance companies, which focused their commercial efforts on the middle and upper classes, which had so far remained outside the health insurance system. Through the study of the VITA, life insurance company from Zurich, I study the strategic motivations which led companies to diversify their activities towards health insurance coverage, and the rationalizing influence that this new competition exerted on the mutuals.