Canine RANKL (Receptor Activator of Nuclear Factor κB Ligand, also known as TNFSF11, TRANCE, or OPGL) is a cytokine belonging to the tumor necrosis factor (TNF) superfamily, which includes related ligands such as TNF-α, Fas ligand (FasL), CD40 ligand (CD40L), and TRAIL that regulate immune signaling, apoptosis, and cellular differentiation. In dogs (Canis lupus familiaris), RANKL is expressed primarily by osteoblasts, bone marrow stromal cells, activated T lymphocytes, and other immune cells, and plays a key role in bone remodeling and immune regulation. RANKL functions by binding to its receptor RANK (receptor activator of NF-κB) on osteoclast precursors and mature osteoclasts, activating intracellular signaling pathways including NF-κB, MAPK, and NFATc1, which promote osteoclast differentiation, activation, and bone resorption. The activity of RANKL is tightly controlled by osteoprotegerin (OPG, TNFRSF11B), a soluble decoy receptor that binds RANKL and prevents its interaction with RANK, thereby regulating bone turnover. In canine health, the RANKL–RANK–OPG signaling axis is important for skeletal development, bone remodeling, and calcium homeostasis, and dysregulation of this pathway has been associated with bone loss disorders, periodontal disease, and osteolytic processes associated with bone tumors such as osteosarcoma. Because dogs are also used as comparative models for human bone diseases and osteosarcoma, canine RANKL is studied in veterinary orthopedics, oncology, and bone biology research, contributing to understanding of osteoclast regulation and skeletal disease.