Fibroblasts are increasingly acknowledged as key contributors to the development of pulmonary vascular disease (PVD), including pulmonary hypertension (PH). Located in the vascular adventitia, these cells undergo early and sustained activation in response to vascular injury and stress signals. They play a significant role in vascular remodeling by proliferating, evading apoptosis, and producing pro-inflammatory factors and extracellular matrix (ECM) proteins. Their continuous activation is maintained by intricate regulatory pathways that encompass metabolic alterations, epigenetic changes, and transcriptional regulation. This chapter investigates the pathological traits of fibroblasts in PH, examines the molecular signaling pathways involved in their activated behavior, and highlights critical areas for future research that may lead to novel therapeutic strategies for preventing and treating PH.