This book is intended for researchers, graduate students and engineers in the fields of structure-borne sound, structural dynamics, and noise and vibration control.Based on vibration differential equations, it presents equations derived from the exponential function in the time domain, providing a unified framework for structural vibration analysis, which makes it more regular and normalized. This wave propagation approach (WPA) divides structures at "discontinuity points," and the waves show characteristics of propagation, reflection, attenuation, and waveform conversion. In each segment of the system between two "discontinuity points," the governing equation and constraint are expressed accurately, allowing the dynamic properties of complex systems to be precisely obtained.Starting with basic structures such as beams and plates, the book then discusses theoretical research on complicated and hybrid dynamical systems, and demonstrates that structural vibration canbe analyzed from the perspective of elastic waves by applying WPA.