GVHD, a major complication post-allogeneic HSCT, involves acute (aGVHD) and chronic (cGVHD) forms, with distinct inflammatory and autoimmune/fibrotic features, respectively. Prevention strategies include CNI with MTX or MMF, ATG, PTCy, and graft manipulation. First-line treatment for aGVHD is corticosteroids, with Ruxolitinib for steroid-refractory cases. cGVHD treatment focuses on symptom control and preventing progression, with ECP and Ruxolitinib as options. Research highlights the importance of microbiota, biomarkers, and novel therapies targeting immune and non-immune pathways for improved outcomes.