B-1 cells constitute a unique subpopulation of normal B lymphocytes and have been shown over the past few decades to engage in functional activities beyond the generation of germline-like natural antibody. These functions include phagocytosis that parallels macrophage function, antigen presentation that rivals dendritic cell activity, and immunosuppression that recalls the role of regulatory T cells. This Annals volume presents a collection of papers stemming from the conference “B-1 Cell Development and Function,” held June 2014 in Tarrytown, New York, and organized by Nichol E. Holodick and Eliver Ghosn, and cochaired by Thomas L. Rothstein and Leonore A. Herzenberg. These papers discuss the nature of B-1 cells in rodents, humans, and nonhuman primates, and include results on early B-1 cell development from non-hematopoietic stem cell hemogenic sources, and on regulation of B-1 cell numbers and expansion by transcription factor, miRNA, cyclin-dependent kinase, and specific receptor elements. The unique antimicrobial and homeostatic roles of B-1 cell–generated IgM, IgA, and IgG antibodies are highlighted, along with the potential fate-determining role of surface immunglobulin specificity. Further discussion revolves around novel phenotypic subdivisions of B-1 cells and unique B-1 cell functional characteristics of phagocytosis, antigen presentation, and immunosuppression. The susceptibility of B-1 cells to malignant transformation is also addressed.