The pathways leading to the development of different dendritic cell (DC) subsets have long been unclear.In recent years,a number of precursors on the route to DC development,both under steady state and inflammatory conditions,have been described,and the nature of these pathways is becoming clearer.In addition,the development of various knockout mouse models and an in vitro system modelling DC development have revealed the role of numerous cytokines and transcription factors that influence DC development.Here,we review recent findings on the factors important in DC development in the context of the developmental pathways that have been described.