Langerhans' cells (LCs) are a special subset of dendritic cells (DCs) in the skin and they form a contiguous network to survey foreign antigens as sentinels in the epidermis. As professional antigen-presenting cells, they capture and process antigens, and migrate to draining lymph nodes to prime naive T cells, thereby playing a central role in integrating cutaneous immune reactions. The functions of LCs are influenced greatly by the microenvironment of the skin, in particular by keratinocytes. Recent studies, however, suggest that LCs may not sense some pathogens and may be dispensable for induction of immunity in some settings of contact hypersensitivity reactions and cutaneous viral infection models. LCs may instead be involved in the induction of Treg cells and peripheral tolerance. The role of LCs needs to be assessed in their interplay with dermal DCs, which have redundant functions with LCs and other immunocompetent cells in the skin.