Regulatory B-cells (Breg cells) represent as an important modulator of the immune system and their role is unique in autoimmunity, infection, tolerance to transplants, allergy, and cancer. Several regulatory mechanisms exist by which Breg cells can control the function of other immune cells through two main pathways: the secretion of soluble molecules and the use of cell surface-expressed molecules. Anti-inflammatory cytokine interleukin-10 acts as the hallmark of Breg cell function; other cytokines with a similar role include the transforming growth factor-beta and interleukin-35. Breg B cells also release the cytotoxic granzyme B that mediates cell apoptosis. Cell surface-expressed proteins include FasL, CD80, CD86, CD73, CD1d, and PD-L1. The present article reviews the immunosuppressive pathways in order to understand how they emerge and are induced to evoke their regulatory activities, and how we can benefit from them in the field of immunotherapy.