This article is a comprehensive review of mycosis fungoides (MF), the most common type of cutaneous T-cell lymphoma. The first portion of the article introduces epidemiologic features of MF. Next, the clinical presentation is described, followed by the microscopic features. This article addresses how to establish a diagnosis of MF and includes a discussion of the utility of ancillary testing, such as immunohistochemistry and T-cell clonality testing. The differential diagnosis is also discussed, with attention to how to distinguish MF from histopathologic mimics. The final section of the article discusses prognosis and risk of disease progression in MF.