Focusing on the theory and state-of-the-art technologies of ultrasonic testing (UT), this book examines ultrasonic propagation in solids and its detection applications, and explores the intersection of UT technology with various fields of electromagnetics, optics and physics. UT is one of the most widely used nondestructive testing techniques due to its high performance in terms of detection efficiency and safety. The rapid development of modern industrial products and technologies has created a new challenge and demand for ultrasonic nondestructive testing technology. This book introduces the fundamentals of UT, including sound wave and sound field, interface wave theory and liquid-solid coupled sound field. It then discusses various types of UT methods, ranging from the critically refracted longitudinal wave method to ultrasonic surface wave and ultrasonic guided wave detection methods. Some newly developed UT techniques are also discussed, including phased-array UT, high-frequency UT and non-contact UT. This title will appeal to engineering students and technicians in the field of ultrasonic nondestructive testing.