Kantianism is a system of critical philosophy developed by Immanuel Kant, as well as other philosophical systems that arose under the influence of his ideas. The term "Kantianism" or "Kantian" is sometimes also used to describe contemporary positions in philosophy of mind, epistemology, and ethics.

The publication of the main works of Kant caught the attention of German intelligentsia. Kant did not go unnoticed, he was read, argued about, admired and said to be the new Moses, Socrates and Luther. Kantianism was born in the 1780s. The influence of Kant's philosophy is seen in historical and philosophical studies, in the theory of law, philosophy of religion, in aesthetics and other disciplines. A large number of works devoted to Kantian philosophy were published, including numerous "extracts", comments, notes and encyclopedic dictionaries of Kant's terms. The first representatives of Kantianism were Reinhold, who published Letters on the Kantian Philosophy (1786), as well as Fichte, whose anonymous work, The Experience of Criticism of All Revelation (1791), was perceived by the public as Kantian. At the same time, the appearance of such works was caused not only by the great praise for the writings of Kant or the depth and originality of his philosophy, but by the extreme complexity and ambiguity of his language, by the difficulty in perceiving the text, about which even the most ardent admirers and friends of the thinker complained. This circumstance prompted him to write in 1784 a condensed and more accessible exposition of the Critique of Pure Reason in Prolegomena to Any Future Metaphysics, and then to the creation of the second version of the Critique in 1787, where he, in addition to making a number of meaningful changes, tried to reduce the difficulties and ambiguities in the presentation, improve it and make it clearer, in order to eliminate misunderstandings that even by knowledgeable and impartial judges helped brave and bright minds to master his sciences.

Nevertheless, Kant’s followers misinterpreted his thoughts and brought forth their own ideas, and the anti-dogmatic attitude and critical method of Kant's philosophy forced people to apply criticism even to Kant. Thus, at first, instead of a harmonious system of Kantianism, German classical philosophy developed, one of the first representatives of which was the Kantian Fichte. An original even by the standards of polymorphic German classical philosophy was the philosophy of Arthur Schopenhauer, which for many reasons can be considered Kantian. The followers of Kant created their own original concepts (Hegelianism) and for a time overshadowed Kant himself, until Otto Liebmann called on the German philosophers to return to Kant (1865).

In the mid-1860's Kantianism has grown into Neo-Kantianism. The largest cities of Neo-Kantianism were the German cities of Marburg and Freiburg, which gave their name to the two largest schools of philosophy. The main object of criticism of neo-Kantianism was Kant's doctrine of an objectively existing, but unknowable thing in itself, which began to be interpreted as the "ultimate concept of experience." Thus, the dualism of Kantian philosophy was eliminated. Neo-Kantianism states that man creates the world in his imagination, which influenced the formation of empirio-criticism. Unlike competing Hegelianism, Neo-Kantianism was inclined to dialogue with science. Its representatives welcomed the first scientific studies on the psychology of perception, as they confirmed Kant's teaching about a priori forms of cognition (Helmholtz, Nelson). Neo-Kantianism also made a significant contribution to the development of scientific methodology, separating humanitarian knowledge from natural science. Within its framework, a philosophical science emerged as axiology.

Having come into contact with the fashionable hobbies of socialist ideas, neo-Kantianism gave birth to the concept of ethical socialism, which found its political expression in Austro-Marxism (Adler). Neo-Kantians perceived socialism as an unattainable moral ideal of society, the path to which lies through gradual social reforms. The Polish philosopher Bochenski noticed that geographically Neo-Kantianism was limited by the borders of Germany, and after the Nazis came to power (1933), it was persecuted, since "the majority of its representatives were of Jewish origin" and adhered to the social democratic convictions (the doctrine of ethical socialism).