C-X-C chemokine receptor type 4 (CXCR4, CD184) is a member of the Class A (rhodopsin-like) G protein-coupled receptor (GPCR) family and serves as the primary receptor for CXCL12, also known as stromal cell-derived factor-1 (SDF-1). As one of the most extensively studied chemokine receptors, CXCR4 plays a central role in regulating cell migration, tissue homing, immune surveillance, embryonic development, hematopoiesis, and stem cell maintenance. Upon binding CXCL12, CXCR4 activates multiple intracellular signaling pathways, including PI3K/AKT, MAPK/ERK, JAK/STAT, PLC/PKC, and Rho GTPase signaling, thereby controlling cell survival, proliferation, chemotaxis, cytoskeletal remodeling, and adhesion. Importantly, CXCR4 is recognized as one of the two principal co-receptors utilized by human immunodeficiency virus type 1 (HIV-1) for host cell entry. X4-tropic HIV-1 strains exploit CXCR4 together with CD4 to infect target T cells, making CXCR4 a longstanding focus of antiviral research.