The peripheral nervous system plexuses include the cervical, brachial, lumbar, sacral, and coccygeal plexuses; of these, the lumbar and sacral plexuses typically are discussed as a single entity, the lumbosacral (LS) plexus. Through the brachial and LS plexuses, nerve fibers pass to all four extremities and the shoulder and pelvic girdles. Consequently, patients with neoplastic plexopathies have significantly impaired quality of life. This chapter begins with a review of plexus anatomy and lesion classification, followed by the various types of tumor classification utilized. The World Health Organization categorizes peripheral nerve tumors into four groups: neurofibromas, schwannomas, perineuriomas, and malignant neural sheath tumors. The remainder of the chapter focuses on clinically relevant information, including the differential diagnosis of neoplastic plexopathies, their evaluation and management, and prognostication. Throughout these sections, specific neoplastic disorders and treatment complication (e.g., radiation plexopathy) will be discussed. The chapter ends with prognostication and future perspectives.