Mycosis fungoides (MF) is the most common primary cutaneous T-cell lymphoma variant and is closely related to a rare leukemic variant, Sézary syndrome (SS). MF patients at risk of disease progression can now be identified and an international consortium has been established to address the prognostic relevance of specific biologic factors and define a prognostic index. There are a lack of randomized clinical trial data in MF/SS and evidence is based on a traditional “stage-based” approach; treatment of early-stage disease (IA-IIA) involves skin directed therapies which include topical corticosteroids, phototherapy (psoralen with UVA or UVB), topical chemotherapy, topical bexarotene, and radiotherapy including total skin electron beam therapy. Systemic approaches are used for refractory early-stage and advanced-stage disease (IIB-IV) and include bexarotene, interferon α, extracorporeal photopheresis, histone deacetylase inhibitors, and antibody therapies such as alemtuzumab, systemic chemotherapy, and allogeneic transplantation. However, despite the number of biologic agents available, the treatment of advanced-stage disease still represents an unmet medical need with short duration of responses. Encouragingly, randomized phase 3 trials are assessing novel agents, including brentuximab vedotin and the anti-CCR4 antibody, mogamulizumab. A broader understanding of the biology of MF/SS will hopefully identify more effective targeted therapies.