The Critique of Practical Reason is the second of Immanuel Kant's three critiques, published in 1788. Hence, it is sometimes referred to as the "second critique". It follows on from Kant's first critique, the Critique of Pure Reason, and is one of his major works on moral philosophy. While Kant had already published one significant work in moral philosophy, the Groundwork of the Metaphysics of Morals (1785), the Critique of Practical Reason was intended to develop his account of the will as determinable by the moral law alone, place his ethical views within the larger framework of his system of critical philosophy, and expand on certain themes in his moral philosophy such as the feeling of respect for the moral law and the concept of the highest good.

Immanuel Kant was a German philosopher and one of the central Enlightenment thinkers. Born in Königsberg, Kant's comprehensive and systematic works in epistemology, metaphysics, ethics, and aesthetics have made him one of the most influential and controversial figures in modern Western philosophy, being called the "father of modern ethics", the "father of modern aesthetics", and for bringing together rationalism and empiricism earned the title of "father of modern philosophy".