Dendritic cells (DC) are located at the environment-host interface and are continuously exposed to a vast array of foreign proteins and pathogens. The major role of DC is to sample environmental antigens and then to migrate to regional lymph nodes where they present processed antigenic peptides to T cells. Therefore, DC can polarize naive T cells into either Th1 or Th2 effector cells and have a central role in coordinating the balance between immunity and tolerance to inhaled antigens. DC studies can be difficult to perform, because there is no specific cell surface marker for DC. Furthermore, they are a minor population in blood and tissue, and show heterogeneity (many subtypes) and remarkable functional plasticity (immature and mature types). Many DC experiments performed in mouse models may be very different in human disease. There are still unknown questions regarding origin, function, and the molecular events governing their characteristic features. Therefore, better understanding of human DC biology will allow us in the future to use DC as a new therapeutic target for refractory airway diseases including asthma, allergic rhinitis and chronic rhinosinusitis with polyposis.