This is the first monograph to comprehensively cover the effect of using power ultrasound to refine and solidify aluminium and magnesium alloys. The author is widely regarded as a pioneer in the field, and the text is based on results obtained over the 40 years he has spent developing these techniques. Ultrasonic treatment efficiently removes hydrogen and fine solid inclusions from melts, and also helps create a refined grain structure during solidification in the ultrasonic field. Both the fundamental and applied aspects of the formation of an extremely fine nondentritic grain structure are discussed, as well as the application of ultrasound to the process of zone melting.