This book reports on cutting-edge applied research and methods in heat and mass transfer and computational fluid dynamics. With a special emphasis on computational methods, it covers applications to different fields, including mechanical engineering, aerospace, and energy, among others. Some relevant experimental validations are described as well. Being the first volume of the two-volume proceedings of the 15th International Conference on Computational Heat and Mass Transfer (ICCHMT 2025), held on May 19-22, 2025, in Antalya, Türkiye, this book offers a timely perspective of research and applications in the field of computational heat and mass transfer. It also provides both academics and professionals with extensive information and a source of inspiration for new developments and collaborations.