This manuscript reviews selected topics in primary immunodeficiency diseases (PIDDs) published in 2017. These include (1) the role of follicular T cells in the differentiation of B cells and development of optimal antibody responses; (2) impaired nuclear factor κB subunit 1 signaling in the pathogenesis of common variable immunodeficiency, revealing an association between impaired B-cell maturation and development of inflammatory conditions; (3) autoimmune and inflammatory manifestations in patients with PIDDs in T- and B-cell deficiencies, as well as in neutrophil disorders; (4) newly described gene defects causing PIDDs, including exostosin-like 3 (EXTL3), TNF-α–induced protein 3 (TNFAIP3 [A20]), actin-related protein 2/3 complex-subunit 1B (ARPC1B), v-Rel avian reticuloendotheliosis viral oncogene homolog A (RELA), hypoxia upregulated 1 (HYOU1), BTB domain and CNC homolog 2 (BACH2), CD70, and CD55; (5) use of rapamycin and the phosphoinositide 3-kinase inhibitor leniolisib to reduce autoimmunity and regulate B-cell function in the activated phosphoinositide 3-kinase δ syndrome; (6) improved outcomes in hematopoietic stem cell transplantation for severe combined immunodeficiency (SCID) in the last decade, with an overall 2-year survival of 90% in part caused by early diagnosis through implementation of universal newborn screening; (7) demonstration of the efficacy of lentiviral vector–mediated gene therapy for patients with adenosine deaminase–deficient SCID; (8) the promise of gene editing for PIDDs using CRISPR/Cas9 and zinc finger nuclease technology for SCID and chronic granulomatous disease; and (9) the efficacy of thymus transplantation in Europe, although associated with an unexpected high incidence of autoimmunity. The remarkable progress in the understanding and management of PIDDs reflects the current interest in this area and continues to improve the care of immunodeficient patients.