Fibroblast activation protein (FAP)-targeted PET/CT has been shown to provide high-contrast visualization of stromal activation across numerous desmoplastic tumors, being increasingly used in oncology. As interpretation challenges arise from benign fibroblastic processes, structured reporting is becoming indispensable. Although early explorations of FAP-targeted radionuclide therapy demonstrate feasibility, therapeutic translation remains constrained by rapid tracer washout and a lack of robust clinical trials. This review summarizes current FAP imaging applications along with theranostic approaches. Moreover, we will also shed light on the concept of image-guided strategies, where FAP PET can potentially determine the retention capacities in-vivo before on-set of novel nonradiolabeled, FAP-targeted drugs.