The Metaphysics of Morals (1797) is Immanuel Kant's final major work in moral philosophy, expanding upon foundational ideas from his Groundwork and Critique of Practical Reason. This significant text is divided into two main sections: the Doctrine of Right and the Doctrine of Virtue.

The Doctrine of Right, published separately in January 1797, focuses on political rights and external conduct, presenting a republican interpretation of civil society and a system of law to ensure individual freedoms. It introduces the universal principle that "Any action is right if it can coexist with everyone's freedom in accordance with a universal law," covering topics like property rights and state law.

Conversely, the Doctrine of Virtue, released in August 1797, delves into ethical theory and internal moral requirements. It develops Kant's conception of virtue and specific ethical duties we hold as rational beings, emphasizing the importance of treating humanity as an end in itself. Kant analytically classifies these duties as perfect or imperfect, and as duties towards ourselves or others.

Though not as widely known as his earlier works in the English-speaking world, The Metaphysics of Morals offers Kant's most mature reflections on peace, law, and the comprehensive framework of ethical duties, distinguishing between moral requirements that allow some flexibility and those that are strict.