The dominant influence was the Bauhaus movement in Germany. Its principles - minimalist forms, rhythmic repetition, no excess ornament, a synthesis of aesthetic and function, attention to sunlight and hygiene - met a pre-existing Lithuanian architectural tradition and produced a recognizably local hybrid. Kaunas modernism is marked by vertical lines, tall narrow windows on public buildings, and a fondness for rounded corners with curved windows that, walking the city today, you can pick out from a hundred meters away. The architect roster mixes Lithuanian names with refugees: Vladimiras Dubeneckis (1888-1932), a Russian who fled Soviet repression; Karolis Reisonas (1894-1981), a Latvian; Arnas Funkas (1898-1957), born in Smolensk and educated in Berlin. Lithuanian-born architects Vytautas Landsbergis-Zemkalnis, Stasys Kudokas, Mykolas Songaila, Feliksas Vizbaras, and Anatolijus Rozenbliumas filled out the central group. The city's overall development plan was drawn up by engineer Antanas Jokimas.

The work was practical before it was beautiful. Lithuania needed a modern hospital - so the Kaunas Clinics complex was approved in 1936 and finished in 1939, on the edge of the Zaliakalnis district, just before the war. It needed schools - the Jonas Jablonskis Gymnasium (1931), the Third Kaunas Gymnasium (1937), the Sixth Kaunas Gymnasium (1938) by Stasys Kudokas. Each used wide window openings to flood classrooms with northern light, a functionalist priority taken seriously. National minorities built their own schools in the same modernist idiom: the Kaunas Jewish Real Gymnasium (1931), considered at the time one of the most beautiful school buildings in all of Lithuania; the German Real Gymnasium (1930) by Landsbergis-Zemkalnis; the Russian Gymnasium (1925); the Polish Adam Mickiewicz Gymnasium (1931). Banks rose along Laisves Aleja, the city's main avenue: the Bank of Lithuania (1928) by Mykolas Songaila, the Land Bank (1935) by Reisonas, the Kaunas Chamber of Commerce and Industry (1939) by Landsbergis-Zemkalnis. The Pazanga building (1934) by Feliksas Vizbaras and the Pienocentras headquarters (1934, also Landsbergis-Zemkalnis) became the first true multi-story buildings in Lithuania - locally nicknamed skyscrapers against a city of two-story houses.

Some of the most ambitious commissions came from the new state's institutions. The Building of the Officers' Club of the Kaunas Garrison, designed by Vladimir Dubeneckis and built between 1931 and 1937, combined functionalist geometry with carved folk-art motifs - a deliberate fusion of European modernism and Lithuanian tradition. The Kaunas Sports Hall went up in just four winter months in 1939 to host the European Basketball Championship, after Lithuania's national team won the 1937 EuroBasket: architect Anatolijus Rozenbliumas designed a hall for 11,000 spectators, praised at the time as one of the most advanced facilities of its kind in Europe. The Christ's Resurrection Basilica, planned from 1926 by Karolis Reisonas as a national pantheon, required public donations that came in slowly - construction stalled, restarted, stalled again, and the building was not consecrated until 2004, sixty-five years after groundbreaking. The Vytautas the Great War Museum, the M. K. Ciurlionis National Art Museum and the Kaunas Carillon tower together formed Unity Square, the new ceremonial center of the temporary capital.

The Soviet occupation of Lithuania in 1940 ended the project. Construction stopped. Many architects were arrested, deported, or fled west; Stasys Kudokas reached the United States, where he continued to practice. During the Nazi occupation that followed, Kaunas's Jewish community - including those who had built the Jewish Real Gymnasium and the Central Jewish Bank - was murdered, mostly at the Ninth Fort and in the Kaunas Ghetto in Vilijampole, where the synagogue ruins still stood when Lithuania regained independence. After the war, Soviet authorities reused the modernist buildings for warehouses, factories, communal apartments, and offices, often gutting the interiors. Many were poorly extended; some were demolished. Despite that, an unusually high proportion survived. After 1990, restoration began under the city municipality.

In 2015, the European Heritage Label recognized 44 of the surviving buildings. That recognition launched a UNESCO nomination, and on 23 September 2023 the World Heritage Committee inscribed 'Modernist Kaunas: Architecture of Optimism, 1919-1939' on the World Heritage List. Architectural historian Marija Dremaite has described the style's defining characteristic as exactly that: optimism, confidence, and the belief that a small new nation could build itself a future at the speed of poured concrete. From above, central Kaunas reads as a unified piece of urban design, with Laisves Aleja running as a long green axis, Unity Square as the deliberate ceremonial center, and the rounded corners and tall narrow windows visible at almost every block. The Sugihara House, a small 1939 modernist villa on Vaizganto Street that served as the Japanese Consulate, holds its own corner of memory - it was here that Chiune Sugihara, against orders from Tokyo, issued thousands of transit visas in summer 1940 that allowed Lithuanian and Polish Jews to escape across the Soviet Union. A modernist house, doing modernist work, in a city that had built itself for exactly that kind of moment.