This paper presents the different utilitarian approaches to ethics. It stresses the influence of utilitarianism in economics in general and in welfare economics in particular. The key idea of the paper to explain the evolution from classical utilitarianism to preferences utilitarianism and towards post-welfarist approaches is the following. Utility is defi-ned normatively and positively. This generates some serious tensions. Utilitarianism needs to evolve to go beyond this ethical tension. Another idea defended in this paper is that the solutions developed by utilitarianism to solve the ethical issue eventually reinforces operational problems. This raises a legitimacy issue as whether the intervention of utilitarian economists in public decision are likely to be normatively transparent.