Zenitism was the first, originally Yugoslav, avant-garde movement articulated in Zagreb and Belgrade in 1921–1926. Its spiritus movens was Ljubomir Micić (1895–1971), writer, promotional critic and theorist of avant-garde, editor of the Zenitist publications. As a stronghold of the Zenitist movement and an international platform for the exchange of ideas between progressive intellectuals and artists of various specialties, Zenit played a key role in profiling the artistic ideology and practice of Zenitism. Based upon the synthesis of different artistic disciplines, styles and genres, as well as new media, the production of this movement had a syncretic, experimental, and transnational character. Although he entered the Zenitist circle as a high school student and a member of the experimental theater group Traveller in 1922, Josip Seissel (1904–1987) — later, in the context of Zenitism, known as Jo Klek — established himself as one of the leading exponents of the movement. His artistic production essentially marked the mature, Belgrade phase of Zenitism (1923–1925). Apart from leaving his trace in the Yugoslav art with his first abstract paintings (PaFaMa, 1922) and intermedial works created in the Constructivist manner, inventively conceived posters and designs of the Zenitist publications, costume sketches and scenography for the Zenitist theater — Klek was also the author of several visionary projects of the Zenitist architecture created at the very beginning of his studies at the Faculty of Engineering in Zagreb. These achievements were preceded by the “paper architecture” (house models) and several drawings, watercolors, tempera and collages (The Bayadera and Playing Cards, 1923; Tavern, 1924), adorned with motives of a fictitious architecture and urban ambiences, articulated on the principles of dynamism, simultaneism, juxtaposition and fragmentation, inherent to new visual media and mass media (film, photography, radio, poster, advertising). Klek’s draft for the construction of The Advertising (1923), his utopistic designs for Zeniteum 1 and Zeniteum 2 (1924), as well as for the Villa Zenit (1924/25) remain the outstanding examples of the Zenitist architecture. Its closest conceptual and formal analogies can be found in the innovative architectural concepts of Expressionism, Cubism, Futurism, De Stijl, Purism, Russian Constructivism, and the Bauhaus. In the context of the Yugoslav interwar period art scene, these projects represented not only a formal-linguistic innovation, but also a kind of conceptual-ideological paradigm that laid the foundation for a new understanding of the social function of architecture. However, having existed exclusively in the form of a conceptual project and outside the context of the established trends in Yugoslav architecture, they could not lead to any significant shifts in local architectural practice of the 1920s and 1930s. Although unrealized, Klek’s architectural projects represent a problematically current and authentic contribution to the avant-garde architectural discourse in Europe.