This is the first book in the new Thermal and Fluid Physics and Engineering series, edited by Professor G. F. Hewitt. This volume, edited by Professor G. P. Celata, explores microchannels. Microchannels have a range of applications, particularly in the context of cooling of electronic equipment. The book fills a void in the existing literature and covers a large body of new knowledge in the thermal-fluid dynamics theory and applications in micro-geometries. The volume also presents a critical assessment of the state-of-the-art in the field. Intended for both academic and industrial audiences.