The regulatory T cells are a subpopulation of T cells which modulate the immune system, maintain tolerance to self-antigens, and abrogate autoimmune disease. T-regs are immunosuppressive in nature and generally suppress induction and proliferation of effector T cells. Several subsets of regulatory T cells includes naturally occurring CD4+ CD25+ T-Reg Cells, antigen-induced TR-1 and TH3 cells, antigen-specific CD4+ T-Reg cells, CD8+ T-Reg cells, TCR γδ+ T-Reg cells etc. Regulatory T cell show some surface molecule or marker like CD4, CD25, CTLA4, GITR and FOXP3. It can also suppress a variety of immune cells including B cells, NK cells, NKT cells, as well as monocytes and dendritic cells. It works gently through some immunosuppressive cytokines such as TGF-β, IL-10, IL-35 etc. This review is thus based on the generation and several functional aspects of regulatory T cell in immune system regulation.