Chicken Interleukin-7 (chIL-7) is a critical lymphopoietic cytokine that plays a central role in the development, survival, and homeostasis of T cells and, to a lesser extent, B cells in avian species. In chickens (Gallus gallus), IL-7 is primarily produced by stromal and epithelial cells within primary lymphoid organs, including the thymus and bursa of Fabricius, and signals through the IL-7 receptor complex composed of IL-7Rα (CD127) and the common gamma chain (γc), activating JAK/STAT pathways—particularly STAT5—to promote lymphocyte proliferation, differentiation, and survival. IL-7 is essential for thymocyte development and peripheral T-cell maintenance, making it fundamental to adaptive immune competence in poultry. Altered IL-7 expression can impact immune development, vaccine responsiveness, and resistance to infectious diseases such as avian influenza, Newcastle disease, and infectious bursal disease. In poultry health and research settings, characterization of chicken IL-7 supports studies of lymphoid organ development, immune reconstitution, vaccine enhancement strategies, and genetic selection for improved disease resistance, reinforcing its importance in both basic avian immunology and commercial poultry production.