Osteopontin (OPN), also known as secreted phosphoprotein 1 (SPP1), is a multifunctional glycoprotein that is expressed in various tissues and cell types in humans. OPN plays a critical role in diverse biological processes, including bone remodeling, immune response, inflammation, and tissue repair. In the context of bone metabolism, OPN is involved in regulating osteoclast and osteoblast activity, as well as in the mineralization of bone matrix. OPN also functions as a cytokine and adhesive protein, mediating cell-cell and cell-matrix interactions, and modulating immune cell function and inflammatory responses. Dysregulation of OPN expression has been associated with various diseases, such as osteoporosis, cancer, and autoimmune disorders, highlighting the importance of OPN in physiological and pathological conditions.