An Introduction. This book explores the physics behind the waves and oscillations encountered in nature. The book, which is written from a theoretical point of view, begins with a brief description of a wave. This is followed by basic equations, conservation laws, the concept of phase velocity, group velocity, and dispersion relation. The book also discusses waves in different areas such as optics, electromagnetism, hydrodynamics, magnetohydrodynamics, shock waves, and plasma physics. The book also provides a brief description of different instabilities. This book is aimed at graduate students and researchers working in various