The subject of this research is the peculiarities of the psychological approaches of European experts of the late XIX - early XX centuries (psychiatrists of the so-called “historical psychiatry”), art historians and painters of the XX century, specializing in collection of the works of mentally ill people (or art brut). The historical-comparative method is applied for determination of the specifics of the naive art of Western Europe in the XIX - XX centuries and its comparison with other areas of amateur art of this period. The psychological approach is essential for studying the works of mentally ill people (or art brut) and its key peculiarities. The comparative method allows analyzing the modern forms of art brut and naive art. The novelty consists in outlining the principal psychological approaches of foreign experts with the art brut, the interpretation of which contributes to decoding of all amateur art. Evolution of views stems from determination of similarities between genius and mental disorders, tracing patterns in creative process of the patients, assessment of the ability of a person with mental disorder to creative thinking and invent the object of art prior to learning the artistic beginning. In this regard, the psychological approach revealed the key trends in studying amateur art: from the perspective of Marseille Rege (with his “embryonic” view) to the point of view of Morgenthaller (with his realization of creativity of the patients), and artistic views of Prinzhorn and Dubuffet, who focus on the art criteria: vision of form, color, composition and other formal attributes of an artwork. Thus, the interpretation of art brut becomes a certain “bridge” for understanding the sphere of the naive art.