With increased rates of expansion in cities, there is an increased demand for energy in these areas, and therefore, new methods of using energy must be developed. Without smart energy systems, renewable energy generation cannot be effectively integrated, and supporting technologies such as smart grids, smart metering, and energy storage will also remain unimplemented. This is evident in Smart Energy 4.0 and 5.0, where the Internet of Energy and computational intelligence are at the forefront of the upcoming energy revolution. This chapter focuses on the significance of smart energy technologies as a means of achieving energy efficiencies, resilience, and sustainability of urban cities. The adoption of renewable energy sources also adds to the transition to a decarbonized economy, conforming to the transformation of the energy sector worldwide. Smart cities also employ such concepts as Digital Twins for better planning and management. The application of these technologies not only promotes energy saving but also allows the development of sustainable urban environments. Some of the possible advancements include the use of new materials in energy storage, improving the flexibility of the smart grids, and designing effective frameworks for utilization of data in energy management. With the changing energy scenario, Smart Energy Systems have significant processes towards the development of smart cities with sustainable as well as reliable energy supply systems.