Primary CNS lymphomas (PCNSLs) are defined as non-Hodgkin lymphomas which, at the time of diagnosis, are located exclusively in the brain parenchyma, in the meninges and / or in the spinal cord or in the vitreoretinal area. They occur much more frequently in immunoincompetent patients than in immunocompetent patients. As a rule, it is an aggressive, diffuse large-cell B-cell lymphoma, in which the median survival time without therapy is only a few weeks to months after diagnosis. The therapeutic spectrum of PCNSL is limited by the difficulty of crossing the blood-brain barrier. If this is the case, however, the chemosensitivity is high. Due to the rarity of this tumor disease, most studies are based only on small numbers of patients with limited informative value. Nevertheless, in the last few years, it has been possible to establish promising curative therapeutic approaches that are based on induction and subsequent consolidation therapy and enable high remission rates and several years of progression-free survival. All of these aspects are taken into account in this monograph, which summarizes the current knowledge on the PCNSLs in a compact and informative way.