Fibroblast activation protein (FAP) is a type II transmembrane serine protease belonging to the dipeptidyl peptidase IV family. The protein encoded by the FAP gene is a homodimeric integral membrane gelatinase selectively expressed in reactive stromal fibroblasts of epithelial cancers, granulation tissue of healing wounds, and malignant cells of bone and soft tissue sarcomas. Under physiological conditions, FAP expression is tightly regulated and largely absent in most normal adult tissues, with transient expression observed only in some fetal mesenchymal tissues and wound healing sites. However, in over 90% of common epithelial cancers, including breast, colorectal, pancreatic, and lung carcinomas, FAP is significantly upregulated in cancer-associated fibroblasts (CAFs) within the tumor stroma. This tumor-restricted expression pattern has established FAP as an attractive diagnostic biomarker and therapeutic target. FAP contributes to tumor progression through multiple mechanisms, including extracellular matrix remodeling, promotion of cancer cell invasion and migration, and modulation of immunosuppressive tumor microenvironments. Targeting strategies currently under investigation include FAP-specific chimeric antigen receptor (CAR)-T cells, antibody-drug conjugates, and FAP-activated prodrugs, with several agents entering clinical trials.