This chapter is aimed at giving the reader some introduction to the fundamentals of ultrasound and ultrasonic metal processing. However, we do not aspire to cover all the aspects of acoustics and sonochemistry; instead, we refer the inquisitive reader to more suitable sources like Blitz [1], Rozenberg [2], Flynn [3], Suslick [4], Mason and Lorimer [5], Brennen [6], and Ensminger et al. [7, 8] as well as to numerous papers published over the years by specialized scientific journals like Ultrasonics, Ultrasonics Sonochemistry, Journal of the Acoustical Society of America, and Akusticheskiy Zhurnal (Russian Acoustics Journal).