This paper investigates the transformation of Trešnjevka from a rural suburb into one of the key districts of Zagreb, focusing on changes during a ninety-year period from 1901 to 1991. At the beginning of the 20th century, Trešnjevka was inhabited by nearly 3,000 inhabitants, but immigration caused quick progression of urbanization, especially after the First World War which also contributed to significant development of this area. A key role in this process was played by the train line „Samoborček“, which connected Trešnjevka, that is Zagreb and Samobor. The interwar period saw rapid modernization, which included the construction of infrastructure, such as schools and other public facilities, that supported the needs of the growing community. For example, architect Ivo Zemljak built a modern school on Selska cesta, which has become a symbol of progress and urban development in Trešnjevka. After the Second World War, with the increase in industrial activity and residential construction, Trešnjevka faced further urban challenges. Traditional family houses, such as we find in the planned settlement of „Prva hrvatska štedionica“, were replaced by residential buildings and skyscrapers, which in this area were designed by the architect Slavko Jelinek, who opts for a characteristic approach to design that emphasizes the importance of common spaces, green areas and recreational facilities. These urban and architectural efforts significantly contributed to the improvement of the quality of life of the residents who inhabited Trešnjevka as a „working class“. Through the analysis of the development of Trešnjevka during the 20th century, the paper concludes that this period was crucial for the formation of its urban identity. From a remote suburb without basic infrastructure, Trešnjevka has grown into a vital Zagreb district, whose history of urban planning and architecture bears witness to the dynamic changes that have shaped the modern city.