Glucocorticoids have been used for over 50 years in the treatment of inflammatory and autoimmune diseases and in preventing graft rejection. Today, knowledge of their molecular, cellular, and pharmacological properties allows a better understanding of glucocorticoid-mediated immunosuppression. Glucocorticoids exert both negative and positive effects with a dynamic and bi-directional spectrum of activities on various limbs and components of the immune response. They modulate genes involved in the priming of the innate immune response, while their actions on the adaptive immune response are to suppress cellular (Th1) immunity and promote humoral (Th2) immunity. Interestingly, glucocorticoids can also induce tolerance to specific antigens by influencing dendritic cell maturation and function and promoting the development of regulatory high IL-10-producing T cells. The ex vivo therapeutic use of glucocorticoids could therefore represent an adjuvant treatment to cell therapy in autoimmune diseases, avoiding the long-term deleterious adverse effects of glucocorticoids. Thus, the panoramic view of glucocorticoid actions on the immune system provides an interesting model for characterizing important biological pathways of immunosuppression.