This review discusses energy dissipation and transport in nanoscale devices, focusing on the challenges and recent advances in understanding and managing energy efficiency in nanoelectronics. It begins by highlighting the wide range of power consumption from nanoscale transistors to massive data centers, emphasizing the importance of energy-efficient design. The review then explores energy dissipation in various nanoscale structures, including circuits, silicon transistors, carbon nanostructures, and semiconductor nanowires. It covers concepts of steady-state and transient thermal transport in nanoscale devices with sub-nanosecond switching times, and recent directions in energy transport, such as electrical and thermal conductivity, thermal rectification, and the role of material interfaces. The review discusses energy dissipation in nanoscale circuits, focusing on leakage and active power, and presents the formula for power dissipation in digital circuits. It also examines energy dissipation in nanoscale devices, including diffusive, ballistic, and contact-related phenomena. The review highlights the importance of understanding energy dissipation in nanoscale devices for improving energy efficiency and reducing waste heat, which is a significant challenge in modern electronics. The review also discusses thermal transport in nanoscale devices, including steady-state thermal resistance and transient heat conduction. It explores the impact of device geometry, material thermal conductivity, and interface thermal resistance on thermal performance. The review further examines energy transport in carbon nanotubes, graphene, and nanowires, highlighting their unique properties and potential for energy-efficient nanoelectronics. It discusses the role of optical phonons, thermal conductivity, and energy dissipation mechanisms in these materials. The review concludes with a discussion of the challenges and future directions in energy transport and dissipation in nanoscale devices, emphasizing the need for further research and development to improve energy efficiency and reduce waste heat in modern electronics.This review discusses energy dissipation and transport in nanoscale devices, focusing on the challenges and recent advances in understanding and managing energy efficiency in nanoelectronics. It begins by highlighting the wide range of power consumption from nanoscale transistors to massive data centers, emphasizing the importance of energy-efficient design. The review then explores energy dissipation in various nanoscale structures, including circuits, silicon transistors, carbon nanostructures, and semiconductor nanowires. It covers concepts of steady-state and transient thermal transport in nanoscale devices with sub-nanosecond switching times, and recent directions in energy transport, such as electrical and thermal conductivity, thermal rectification, and the role of material interfaces. The review discusses energy dissipation in nanoscale circuits, focusing on leakage and active power, and presents the formula for power dissipation in digital circuits. It also examines energy dissipation in nanoscale devices, including diffusive, ballistic, and contact-related phenomena. The review highlights the importance of understanding energy dissipation in nanoscale devices for improving energy efficiency and reducing waste heat, which is a significant challenge in modern electronics. The review also discusses thermal transport in nanoscale devices, including steady-state thermal resistance and transient heat conduction. It explores the impact of device geometry, material thermal conductivity, and interface thermal resistance on thermal performance. The review further examines energy transport in carbon nanotubes, graphene, and nanowires, highlighting their unique properties and potential for energy-efficient nanoelectronics. It discusses the role of optical phonons, thermal conductivity, and energy dissipation mechanisms in these materials. The review concludes with a discussion of the challenges and future directions in energy transport and dissipation in nanoscale devices, emphasizing the need for further research and development to improve energy efficiency and reduce waste heat in modern electronics.