Thermal engineering, a cornerstone of modern technology, continues to evolve rapidly in response to the pressing need for sustainable energy solutions and the demand for enhanced performance in various industries. This book explores frontiers in thermal engineering by addressing various fields of research. Researchers are actively exploring nano materials, meta materials, and composites to engineer materials with exceptional thermal conductivity, thermal insulation, and thermal expansion properties. The integration of thermal engineering with sustainability goals is another critical frontier. Researchers are also exploring sustainable cooling solutions, as the demand for air conditioning grows, to reduce energy consumption and environmental impact. Additionally, computational tools and artificial intelligence are enabling more accurate modeling and optimization of thermal systems, leading to increased energy efficiency and reduced emissions. While these frontiers present exciting opportunities, challenges persist. Thermal management in high-power electronics, urban heat island effects, and the efficient utilization of renewable energy sources remain areas of active research.