Type I interferons (IFNs) are key cytokines in the host immune response against viral infections, but they also play a broader role in host defense and homeostasis. This review highlights the immunomodulatory functions of type I IFNs in health and disease, focusing on their roles in innate and adaptive immune responses, bacterial ligand recognition, inflammasome activation, intestinal homeostasis, and inflammatory and autoimmune diseases such as coeliac disease, psoriasis, multiple sclerosis, and cancer. Type I IFNs are produced by various cell types, including leukocytes, fibroblasts, and endothelial cells, and their production is induced by bacterial ligands through TLR-dependent pathways. They activate signaling pathways that lead to the production of IFN α and β, which in turn regulate gene expression and immune responses. Type I IFNs also modulate immune responses by activating STAT1, STAT2, and IRF9, leading to the formation of the ISGF3 complex, which binds to ISRE elements in the promoters of ISGs. They also activate STAT3, which can have different effects depending on the context. Type I IFNs can also induce the production of IL-10, which has anti-inflammatory effects. In addition, type I IFNs can activate other signaling pathways, such as MAPK and PI3K, which are involved in their biological functions. Type I IFNs have been shown to suppress intestinal inflammation by enhancing the barrier function of intestinal epithelial cells and by modulating the activity of dendritic cells. They also play a role in the regulation of adaptive immune responses, including the differentiation of T helper cells and the suppression of T helper 17 cell-mediated responses. Type I IFNs can also inhibit the activation of inflammasomes, such as the NLRP1 and NLRP3 inflammasomes, and can increase susceptibility to certain bacterial infections. In autoimmune diseases, type I IFNs can have both protective and detrimental effects, depending on the disease and the context. In cancer, type I IFNs have been used for the treatment of various types of cancer, but they can also cause severe side effects. Overall, the functions of type I IFNs are complex and context-dependent, and their role in immune-mediated and inflammatory disorders is increasingly recognized.Type I interferons (IFNs) are key cytokines in the host immune response against viral infections, but they also play a broader role in host defense and homeostasis. This review highlights the immunomodulatory functions of type I IFNs in health and disease, focusing on their roles in innate and adaptive immune responses, bacterial ligand recognition, inflammasome activation, intestinal homeostasis, and inflammatory and autoimmune diseases such as coeliac disease, psoriasis, multiple sclerosis, and cancer. Type I IFNs are produced by various cell types, including leukocytes, fibroblasts, and endothelial cells, and their production is induced by bacterial ligands through TLR-dependent pathways. They activate signaling pathways that lead to the production of IFN α and β, which in turn regulate gene expression and immune responses. Type I IFNs also modulate immune responses by activating STAT1, STAT2, and IRF9, leading to the formation of the ISGF3 complex, which binds to ISRE elements in the promoters of ISGs. They also activate STAT3, which can have different effects depending on the context. Type I IFNs can also induce the production of IL-10, which has anti-inflammatory effects. In addition, type I IFNs can activate other signaling pathways, such as MAPK and PI3K, which are involved in their biological functions. Type I IFNs have been shown to suppress intestinal inflammation by enhancing the barrier function of intestinal epithelial cells and by modulating the activity of dendritic cells. They also play a role in the regulation of adaptive immune responses, including the differentiation of T helper cells and the suppression of T helper 17 cell-mediated responses. Type I IFNs can also inhibit the activation of inflammasomes, such as the NLRP1 and NLRP3 inflammasomes, and can increase susceptibility to certain bacterial infections. In autoimmune diseases, type I IFNs can have both protective and detrimental effects, depending on the disease and the context. In cancer, type I IFNs have been used for the treatment of various types of cancer, but they can also cause severe side effects. Overall, the functions of type I IFNs are complex and context-dependent, and their role in immune-mediated and inflammatory disorders is increasingly recognized.