The genetic dissection of human primary immunodeficiency is expanding at full speed, in at least two directions. Some investigators pursue the dissection of well-known clinical phenotypes, for which the count of genetic etiologies seems to be endless, whereas others begin the search for inborn errors underlying new phenotypes, infectious and otherwise. The field of primary immunodeficiency is also expanding in other ways, with new therapeutic approaches, and with the care of patients in regions of the world where these diseases were unheard of less than a decade ago. The volume provides an overview of the field of medical genetics and its progress in 2011. Volume I opens with a dialog between the volume editors on the definition of “primary immunodeficiencies (PIDs);” additional papers in this volume focus on PIDs in Latin America, Eastern and Central Europe, North Africa, Turkey, Asia, Iran, and the South Pacific. Volumes II and III focus on new developments in PIDs, insights into PID pathophysiology, and PIDs in India and the Middle East.