This study demonstrates that the presence of diversified corporate forms within the insurance industry does not always lead to the dominance of what is, according to theory, the most efficient business form, the joint-stock corporation. Swedish mutual insurance companies have often been connected to various popular movements, and have thus obtained quasi-monopoly rights for writing certain kinds of insurance. This has been important as a means of obtaining economies of scale and creating efficient organisations, and has allowed them to compete with their joint-stock rivals. Mutuals have also remained important players in the insurance market by keeping policyholders’ interests in focus through creative product diversification and by expanding nationally to reach customers outside of their original base. Mutuality also protected them against hostile take-overs that weakened the stock corporations. Mutual insurers not only survived as independent companies but also were a success.