The categorical imperative (German: kategorischer Imperativ) is the central philosophical concept in the deontological moral philosophy of Immanuel Kant. Introduced in Kant's 1785 Groundwork of the Metaphysics of Morals, it is a way of evaluating motivations for action. It is best known in its original formulation: "Act only according to that maxim whereby you can at the same time will that it should become a universal law."

According to Kant, sentient beings occupy a special place in creation, and morality can be summed up in an imperative, or ultimate commandment of reason, from which all duties and obligations derive. He defines an imperative as any proposition declaring a certain action (or inaction) to be necessary. Hypothetical imperatives apply to someone who wishes to attain certain ends. For example, "I must drink something to quench my thirst" or "I must study to pass this exam." A categorical imperative, on the other hand, denotes an absolute, unconditional requirement that must be obeyed in all circumstances and is justified as an end in itself.

Kant expressed extreme dissatisfaction with the popular moral philosophy of his day, believing that it could never surpass the level of hypothetical imperatives: a utilitarian says that murder is wrong because it does not maximize good for those involved, but this is irrelevant to people who are concerned only with maximizing the positive outcome for themselves. Consequently, Kant argued, hypothetical moral systems cannot persuade moral action or be regarded as bases for moral judgments against others, because the imperatives on which they are based rely too heavily on subjective considerations. He presented a deontological moral system, based on the demands of the categorical imperative, as an alternative.