Dendritic cells (DCs) are a heterogeneous population of professional antigen-presenting cells. Several murine DC subsets have been identified that differ in their phenotype and functional properties. In the steady state, DC precursors originating from the bone marrow give rise to lymphoid-organ-resident DCs and to migratory tissue DCs. During inflammation, an additional DC subset has been described, so-called inflammatory DCs (infDCs), which differentiate from monocytes recruited to the site of inflammation. Here, we review recent work on the development and functions of murine infDCs. We also examine the criteria that define infDCs. Finally, we discuss the characterization of human infDCs and their potential role in inflammatory diseases.