Swine interferon lambda 3 (IFN-λ3), also known as interleukin-28B (IL-28B), is a member of the type III interferon family and functions as a key antiviral cytokine that signals through the IFNLR1 (IL-28Rα)/IL-10R2 receptor complex, activating JAK/STAT pathways and inducing interferon-stimulated genes (ISGs) that restrict viral replication primarily at epithelial surfaces. In swine, IFN-λ3 plays a critical role in mucosal immunity within the respiratory and gastrointestinal tracts, major entry points for economically significant pathogens such as porcine reproductive and respiratory syndrome virus (PRRSV), swine influenza virus (SIV), porcine epidemic diarrhea virus (PEDV), transmissible gastroenteritis virus (TGEV), and porcine deltacoronavirus (PDCoV). Because type III interferons generate localized antiviral protection with less systemic inflammation than type I interferons, swine IFN-λ3 is likely essential for controlling viral spread while preserving tissue integrity and growth performance. As respiratory and enteric viral diseases substantially impact global pork production, swine IFN-λ3 (IL-28B) is highly relevant for understanding antiviral defense mechanisms, improving vaccine strategies, and developing immunomodulatory approaches to enhance herd health and biosecurity.