Although it may seem a simple and obvious notion, Peirce’s conception of ethics has a complexity and richness which grew over the course of his entire intellectual life. The aim of this paper is to discuss three doctrines which have been key to the development of Peirce’s ethics. The first is the notion of final causation, such that ethics is above all a science of purpose, ordered to the ultimate end of human beings. The second is the notion of self-controlled action, insofar as ethics studies the deliberate action, especially from the point of view of its self-criticism and reflective quality. Finally, the third key is the character of normative science, which makes ethics the theoretical-philosophical science of secondness; and the positive science, with an objective basis, that investigates the way to achieving the self-control which will lead to the most elevated and universal ideals.