For many years, it has been considered that the function of B cells is only to serve as precursors of antibody-producing plasma cells; however, this simplistic view has been challenged in the past thirty years. The first big surprise came during the seventies, when it was shown that B lymphocytes are not a homogeneous population, but is made up of various subpopulations with different origin and functions, including both innate and acquired immunity. During the eighties, it was discovered that B cells are an important source of cytokines, extending its functions from antigen presentation to cooperation with T cells. From the year two thousand, it is clear that B cells are, functionally speaking, as heterogeneous as T lymphocytes, extending its functions to the regulation of the immune response. The story does not end yet, as they continue to discover new features that will have to be incorporated into the main body of knowledge about the mechanisms by which the immune response works. Thus, we can conclude by congratulating the B lymphocytes by these first 50 years and we can predict at least another 50 of robust growth.