FDG-PET/CT is central to Lugano-based staging, Deauville-scored response assessment, and prognostication across Hodgkin and non-Hodgkin lymphoma subtypes. Quantitative metrics, particularly total metabolic tumor volume, have emerged as powerful independent prognostic biomarkers. In Hodgkin's lymphoma, interim PET successfully guides treatment de-escalation, while in DLBCL, interim PET remains prognostic but not therapeutically actionable. FDG-PET/Ct is a valuable prognostic biomarker for multi-time point assessment during CAR-T therapy, and guides bridging therapy. More sophisticated PET prognostic and response assessment criteria are emerging in the era of targeted therapies with the help of PET radiomics and deep learning, which needs standardization.