Green cities and smart innovation, where it focuses particularly on how emerging technologies assist in sustainable urbanization. It relies on research that has been published between 2010 and 2025 and explains how the Internet of Things, artificial intelligence solutions, big data, as well as Green Internet-of-Things technology, aid to a great extent in management. It summarises the results into the main themes, such as technology and infrastructure, governance and policy, sustainable practice, data-driven innovation, and urban well-being. They specify the sectors such as energy management, waste minimization, and sustainable transport. It also tackles challenges, such as high infrastructure expenditure, cybersecurity, interoperability, gaps in governance, and digital disparities. The paper finishes with bridging research gaps and demanding integrative frameworks, bringing together technological Innovation, inclusive governance, and citizen engagement to build strong, just, and sustainable urban environmental systems.