Plasmacytoid dendritic cells (pDCs) are a unique subset of dendritic cells that specialize in producing type I interferons (IFNs) in response to viral or self nucleic acids. They play a crucial role in antiviral immune responses and are implicated in autoimmune diseases characterized by a type I IFN signature. However, pDCs can also induce tolerogenic immune responses. This review discusses recent progress in the field of pDC biology, focusing on molecular mechanisms regulating pDC development and functions, pathways involved in sensing pathogens and endogenous nucleic acids, their function at mucosal sites, and their roles in infections, autoimmunity, and cancer. Key topics include the phenotypes of human and mouse pDCs, the development of pDCs, trafficking, innate sensing, regulation by microRNAs and hormones, antigen presentation, and their pathogenic functions in autoimmune diseases. The review highlights the multifaceted biology of pDCs and the ongoing research efforts to understand their complex roles in immune responses and disease.Plasmacytoid dendritic cells (pDCs) are a unique subset of dendritic cells that specialize in producing type I interferons (IFNs) in response to viral or self nucleic acids. They play a crucial role in antiviral immune responses and are implicated in autoimmune diseases characterized by a type I IFN signature. However, pDCs can also induce tolerogenic immune responses. This review discusses recent progress in the field of pDC biology, focusing on molecular mechanisms regulating pDC development and functions, pathways involved in sensing pathogens and endogenous nucleic acids, their function at mucosal sites, and their roles in infections, autoimmunity, and cancer. Key topics include the phenotypes of human and mouse pDCs, the development of pDCs, trafficking, innate sensing, regulation by microRNAs and hormones, antigen presentation, and their pathogenic functions in autoimmune diseases. The review highlights the multifaceted biology of pDCs and the ongoing research efforts to understand their complex roles in immune responses and disease.