Unitary Symmetry and Elementary Particles discusses the role of symmetry in elementary particle physics. The book reviews the theory of abstract groups and group representations including Eigenstates, cosets, conjugate classes, unitary vector spaces, unitary representations, multiplets, and conservation laws. The text also explains the concept of Young Diagrams or Young Tableaux to prove the basis functions of the unitary irreducible representations of the unitary group SU(n). The book defines Lie groups, Lie algebras, and gives some examples of these groups. The basis vectors of irreducible unitary representations of Lie groups constitute a multiplet, which according to Racah (1965) and Behrends et al. (1962) can have properties of weights. The text also explains the properties of Clebsch-Gordan coefficients and the Wigner-Eckart theorem. SU(3) multiplets have members classified as hadrons (strongly interacting particles), of which one characteristic show that the mass differences of these members have some regular properties. The Gell-Mann and Ne-eman postulate also explains another characteristic peculiar to known multiplets. The book describes the quark model, as well as, the uses of the variants of the quark model. This collection is suitable for researchers and scientists in the field of applied mathematics, nuclear physics, and quantum mechanics.