"The Critique of Practical Reason" is a philosophical work written by the German philosopher Immanuel Kant. It was first published in 1788 and is considered one of his most important works.

The book explores the nature of practical reason and ethical decision-making. Kant argues that practical reason is the basis for moral action and that moral action is grounded in a universal principle of reason called the "Categorical Imperative". He argues that moral decisions cannot be based on personal preferences or desires, but rather on the rational principles that guide human behavior.

The book is divided into two main parts. The first part focuses on the "Analytic of Pure Practical Reason", which explores the nature of practical reason itself. The second part, the "Dialectic of Pure Practical Reason", examines the application of practical reason to ethical decision-making.

Overall, "The Critique of Practical Reason" is a dense and complex philosophical work that offers a comprehensive analysis of the nature of practical reason and its role in ethical decision-making. It is an important contribution to the field of moral philosophy and continues to be studied and debated by scholars today.