Follicular lymphoma (FL), the most common indolent non-Hodgkin lymphoma, presents heterogeneous clinical behavior, recurrent relapses, and a 2–3% annual risk of histologic transformation to aggressive lymphoma. This chapter comprehensively reviews the role of 18F-fluorodeoxyglucose (18F-FDG) positron emission tomography/computed tomography (PET/CT) in FL management. It is well established that PET/CT significantly refines initial staging compared with conventional imaging leading to stage migration in 15–30% of patients, particularly in those with presumed limited-stage disease; this is driven by its superior detection of occult nodal, extranodal, and bone marrow involvement, with approximately 90% negative predictive value for marrow disease that may, in some cases, reduce the need for biopsy. End-of-induction PET/CT, using Lugano/Deauville criteria, robustly predicts prolonged progression-free survival (hazard ratios 4–5 for non-complete metabolic response), while interim PET is promising. Routine surveillance imaging lacks survival benefit and is not recommended; PET/CT is reserved for clinical or biochemical suspicion of relapse or transformation. Baseline total metabolic tumor volume emerges as the strongest independent prognostic biomarker, outperforming or synergizing with the Follicular Lymphoma International Prognostic Index (FLIPI) or its successor (FLIPI2) and ctDNA to identify very-high-risk subgroups with markedly inferior progression-free survival and early progression (POD24) risk, enabling risk-adapted therapeutic strategies. Overall, 18F-FDG PET/CT has transformed FL from an anatomically staged disease to a metabolically guided entity, facilitating precision prognostication, response-adapted treatment, and improved patient outcomes.