This contribution seeks to answer two related questions. First, what is the purpose of social health insurance? Or put in slightly different terms, what are the reasons for social (or public) health insurance to exist, even to dominate private health insurance in most developed countries? And second, what are the limits of social health insurance? Can one say that there is "too much" social health insurance in the following two senses: Should the balance be shifted towards the private alternative? And is the degree of coverage excessive?