This chapter provides a comprehensive examination of the pivotal role played by the Internet of Things (IoT) in addressing pressing environmental challenges and fostering sustainability of smart cities. It underscores the imperative of innovative strategies for combatting issues such as climate change, habitat degradation, and resource depletion. The IoT, characterized by interconnected devices, sensors, and systems, facilitates real-time data acquisition and analysis, thereby revolutionizing environmental monitoring and management. This work offers a foundational exploration of IoT’s principles within the context of environmental monitoring, encompassing its amalgamation with environmental science, sensor technologies, and data acquisition methodologies. Additionally, the chapter delves into the specific applications of IoT in the realm of environmental sustainability, encompassing domains such as air and water quality monitoring, waste management, and biodiversity conservation. It also conducts a comprehensive analysis of the challenges associated with deploying IoT in environmental monitoring, including critical concerns about data security and privacy. Emerging technologies and trends within the IoT landscape are scrutinized, with a particular emphasis on the convergence of artificial intelligence (AI) and IoT, notably through machine learning algorithms and predictive analytics, for the augmentation of environmental monitoring capabilities. In conclusion, this chapter underscores the transformative potential inherent in IoT for addressing complex environmental issues in smart cities. It advocates for continued research and innovation in this field, asserting that the fusion of IoT and AI holds the promise of deeper insights into environmental conditions and the ability to make well-informed decisions in the pursuit of sustainability in smart cities.