Summary: Recent years have seen a major advance in our understanding of the organization of the dendritic cell (DC) compartment. Particularly rewarding in this respect have been studies investigating DC origins, based on the identification of transcription factor and growth factor requirements, as well as direct demonstrations of precursor/progeny relationships by adoptive cell transfers. However, to fully understand the organization of the DC compartment, functional definitions of DC subsets must be provided and potential task divisions revealed that distinguish DC from other immune cells, including the closely related mononuclear phagocytes, such as macrophages. In fact, functional definitions might eventually replace the current distinction between DC and macrophages, which is in part based on arbitrary historic considerations, i.e. mononuclear phagocytes identified before the advent of DC in the mid 1970s generally termed macrophages. In this article, we review recent insight in the functions of classical DC in the mouse, focusing on our own work involving conditional and constitutive cell ablation.