C-methionine (MET) positron emission tomography (PET) is one of the most used nuclear imaging modalities in brain tumors. Because of its characteristics, MET-PET should be able to provide us a high detection rate of brain tumors and good lesion delineation. This book chapter provides a clinical overview of important issues in primary brain tumors, recurrent brain tumors, and brain metastases. The role and dilemmas in neuroimaging are discussed. The working mechanism, scan interpretation, and quantifi cation possibilities of MET-PET are explained. An overview is given of the role of MET-PET in gliomas (diagnostic accuracy, grading, prognosis, and assessment of tumor extent) with special focus on available literature in the role of MET-PET to differentiate between tumor progression/recurrent tumor and radiation necrosis.