The paper reviews the application of non-abelian discrete groups to the theory of neutrino masses and mixing, motivated by the agreement between experimental data and the Tri-Bimaximal (TB) mixing pattern. It discusses specific models based on groups like $A_4$, $S_4$, and others, and their phenomenological implications, including lepton flavor violating processes, leptogenesis, and extensions to quarks. The authors explore both TB mixing and Bimaximal (BM) mixing, which is a related concept. They emphasize the role of discrete flavor symmetries in explaining the observed neutrino mixing patterns and the hierarchy of neutrino masses. The paper also delves into the mathematical structure of these groups, their representations, and how they can be spontaneously broken to produce the observed mixing angles and mass hierarchies. The authors provide detailed examples, such as the $A_4$ model, and discuss the implications for neutrino oscillation experiments and the see-saw mechanism for generating neutrino masses. They conclude by exploring the possible origin of $A_4$ symmetry and its connection to the modular group.The paper reviews the application of non-abelian discrete groups to the theory of neutrino masses and mixing, motivated by the agreement between experimental data and the Tri-Bimaximal (TB) mixing pattern. It discusses specific models based on groups like $A_4$, $S_4$, and others, and their phenomenological implications, including lepton flavor violating processes, leptogenesis, and extensions to quarks. The authors explore both TB mixing and Bimaximal (BM) mixing, which is a related concept. They emphasize the role of discrete flavor symmetries in explaining the observed neutrino mixing patterns and the hierarchy of neutrino masses. The paper also delves into the mathematical structure of these groups, their representations, and how they can be spontaneously broken to produce the observed mixing angles and mass hierarchies. The authors provide detailed examples, such as the $A_4$ model, and discuss the implications for neutrino oscillation experiments and the see-saw mechanism for generating neutrino masses. They conclude by exploring the possible origin of $A_4$ symmetry and its connection to the modular group.