The “Metaphysical Principles of the Doctrine of Virtue” (Metaphysische Anfangsgründe der Tugendlehre) is the second part of the “Metaphysics of Morals” (Metaphysik der Sitten), published by Kant in 1797. This monographic study comments Kant´s Tugendlehre as a refutation of the “formalist” vision of Kant´s Ethics. This late writing is shown as consistent with the moral philosophy already presented in the “Groundwork” and the second “Critique”. The “Doctrine of Virtue” offers Kant´s application of the categorical imperative and acknowledges the conditions of moral motivation and, in general, of human agency. Kant´s derivation of duties of virtue (Tugendpflichten) is attentive to the fundamental characteristics of human nature, therefore it generates a system of ends that reason itself shows to be obligatory for the human faculty of choice. This book shows that Kant´s “Doctrine of Virtue” is worthy of being taken into a greater philosophical consideration.