The rapid urbanization, intensified transportation demand, and environmental pressures of the 21st century necessitate the development of new sustainability-focused solutions in urban management. Smart cities, which have emerged in this context, represent a transformation model that aims to manage urban infrastructure more effectively, use resources efficiently, and improve quality of life through the integration of information and communication technologies (ICT). Intelligent transportation systems (ITS), one of the most critical components of this model, play a strategic role in providing safe, efficient, environmentally friendly, and user-oriented transportation services. This book chapter examines the conceptual framework, basic components, and development dynamics of smart cities; it details the definition, functions, and contributions of ITS in the context of sustainable mobility. Successful application examples from around the world (Curitiba, London, Tokyo, Copenhagen) and Turkey (Istanbul, Ankara, Izmir, Eskisehir) are examined, and the effects of ITS on traffic management, road safety, carbon emission reduction, and making public transportation more attractive are discussed. Furthermore, challenges encountered, such as high investment costs, data security and privacy issues, lack of institutional coordination, and social acceptability, are analyzed. The study also addresses the opportunities that new technologies, such as artificial intelligence, the Internet of Things, digital twin applications, and autonomous vehicles, will create for the development of ITS within a future-oriented perspective. In this context, the central role of ITS in ensuring sustainable mobility in smart cities is emphasized; strategic recommendations at the policy, technological, and societal levels are presented for Turkey to effectively utilize this potential. In conclusion, intelligent transportation systems are not only a technical innovation but also the key to sustainable urban transformation. It is critically important for Turkey to develop a national ITS strategy, prioritize public transportation, strengthen data security and user-oriented mobility services, and build a globally competitive and sustainable transportation infrastructure.