This book discusses acoustic waves in five chapters. Chapter 1 reviews the general properties of waves. Chapter 2 presents the acoustic waves in fluid and solids, including the wave equations in the respective media. Chapter 3 discusses the propagation of audible acoustic waves in the air. The discussion includes analyses of speech and music we hear in the time and frequency domains. Chapter 4 discusses the propagation of acoustic waves in solids. Unlike in the air, sound waves take complicated forms in solids; they can be both in longitudinal and transverse modes, and mode conversions can occur upon reflection. Although these behaviors make the analysis difficult, we can apply them to engineering problems. Chapter 5 describes the transduction of acoustic signals. It presents acoustic transmitters and sensors along with their operation principles. Finally, Chapter 6 presents several techniques used in engineering. It is also useful to consider applying acoustic and optical techniques to engineering problems.