The aim of this study was to analyze the impact of mass tourism on spatial development and mobility in coastal cities of Istria, focusing on Rovinj, Poreč, and Pula. Although mass tourism contributes to economic growth, it creates significant spatial and infrastructural challenges and affects social changes such as gentrification and population outflow. The research was based on the analysis of literature, statistical data, and spatial planning documents, using case studies. The results highlight the seasonality of tourist pressure, urban expansion, land-use changes, apartmentization, and additional strain on transport and communal infrastructure. The discussion emphasizes the need for sustainable spatial planning, regulation of accommodation capacities, and improved mobility. The main contribution of the study is the identification of critical points and the proposal of measures to ensure the long-term quality of life for local residents.