We review pedagogically non-Abelian discrete groups, which play an important role in the particle physics. We show group-theoretical aspects for many concrete groups, such as representations, their tensor products. We explain how to derive, conjugacy classes, characters, representations, and tensor products for these groups (with a finite number). We discussed them explicitly for \(S_N\), \(A_N\), \(T'\), \(D_N\), \(Q_N\), \(\Sigma(2N^2)\), \(\Delta(3N^2)\), \(T_7\), \(\Sigma(3N^3)\) and \(\Delta(6N^2)\), which have been applied for model building in the particle physics. We also present typical flavor models by using \(A_4\), \(S_4\), and \(\Delta (54)\) groups. Breaking patterns of discrete groups and decompositions of multiplets are important for applications of the non-Abelian discrete symmetry. We discuss these breaking patterns of the non-Abelian discrete group, which are a powerful tool for model buildings. We also review briefly about anomalies of non-Abelian discrete symmetries by using the path integral approach.