An Introduction to Elementary Particles, Second Edition aims to give an introduction to the theoretical methods and ideas used to describe how elementary particles behave, as well as interpret some of the phenomena associated with it. The book covers topics such as quantum mechanics; brats, kets, vectors, and linear operations; angular momentum; scattering and reaction theory; the polarization and angularization of spin-0-spin-1/2 scattering; and symettery, isotopic spin, and hypercharge. The book also discusses particles such as bosons, baryons, mesons, kaons, and hadrons, as well as the interactions between them. The text is recommended for physicists, especially those who are practitioners and researchers in the fields of quantum physics and elementary-particle physics.