The article investigates theoretical foundations of the study of such a linguistic phenomenon as idiostyle and its interpretations. The topicality is determined by increasing interest among scholars in studying of individual peculiarities of the writer‘s idiostyle. For this purpose, a number of definitions of the terms ―style‖, ―idiostyle‖, ―individual style‖ are reviewed and analyzed. Idiostyle as a lingual-cognitive portrait of a writer is reflected in his texts and represented by the individual conceptualization of the world, being determined by the individual system of values.The author‘s fictional conceptual system is referred to as the lingual-cognitive basis of his idiostyle. It consists of the thematically related literary concepts verbalized in creative works. In addition, the article dwells on the correlations between idiostyle and other notions such as a world view, individual author‘s conceptual system, individual concepts, dominant and constant of idiostyle. Focusing on functional characteristics of James Joyce‘s individual style of writing as well as their verbalization in the writer‘s prose, this paper is an attempt of creating the portrait of the well-known representative of modernist literature and defining dominant features of his works.