Dendritic cells (DCs) are specialized antigen-presenting cells and essential mediators of immunity and tolerance. This group of cells is heterogeneous in terms of cell-surface markers, anatomic location, and function. Here, we review the development and function of DCs found in lymphoid and non-lymphoid tissues in the steady state. DC and monocyte lineages originate from a common progenitor, the monocyte and dendritic cell progenitor (MDP). The two cell types diverge when MDPs give rise to monocytes and committed DC progenitors (CDPs) in the bone marrow. CDPs give rise to pre-DCs, which migrate from the bone marrow to lymphoid and non-lymphoid tissues to produce the two major subpopulations of lymphoid tissue DCs and non-lymphoid tissue CD103(+) DCs. Within tissues and during development, DC division and homeostasis are regulated by the hormone Flt3L.