This textbook has been designed to meet the needs of B.Sc. Third Semester students of Physics as per Common Minimum Syllabus prescribed for Ranchi University and other Universities and Colleges under the recommended National Education Policy 2020 in Jharkhand. The theory starts with Wave Motion followed by Velocity of Waves, Superposition of Collinear and Two Perpendicular Harmonic Oscillators, Superposition of Two Harmonic Waves, Interference, Interferometer, Fraunhofer Diffraction, Fresnel Diffraction, Polarization of Electromagnetic Waves and Rotatory Polarization. These all are lucidly explained in this book. Short and Long Questions are incorporated at the end of each chapter to build confidence in every student for theory examination. The practical part contains experiments on Refraction, Interference, Diffraction and Polarization. Oral questions are incorporated at the end of each experiment which are useful for Practical examination. These all are lucidly explained in this book.