Modern particle physics research is focused on subatomic particles, including atomic constituents such as electrons, protons, and neutrons (protons and neutrons are composite particles called baryons, made of quarks), produced by radioactive and scattering processes, such as photons, neutrinos, and muons, as well as a wide range of exotic particles. To be specific, the term particle is a misnomer from classical physics because the dynamics of particle physics are governed by quantum mechanics. As such, they exhibit wave-particle duality, displaying particle-like behaviour under certain experimental conditions and wave-like behaviour in others. In more technical terms, they are described by quantum state vectors in a Hilbert space, which is also treated in quantum field theory. The particle theory of light was also proposed by Alhazen, Avicenna, Gassendi, and Newton. These early ideas were founded in abstract, philosophical reasoning rather than experimentation and empirical observation. This book will develop in the student an understanding of the principles of this subject. In order to make the subject simple and interesting every topic included in this book has been self-sufficient in itself and has been explained in the light of modern development in a simple and elegant style.