Epigenetic mechanisms including DNA methylation and histone modifications are critically involved in immune responses. Antigen stimulation along with a specific cytokine milieu drives helper T-cell differentiation into specific subsets with distinct functional capacities. This process occurs by inducing chromatin remodeling and altering transcriptional accessibility of key cytokine genes such as IFN-γ, IL-4 and IL-17. These epigenetic changes, by definition, are carried over throughout cell division to ensure selective survival of a cell lineage. Over the past decade, a growing body of literature mechanistically uncovered the central role for epigenetic regulation in immunity. In this review, we focus on epigenetics in T helper cell differentiation, regulatory T-cell function, and IL-2 production.