T-cell lymphomas are a heterogeneous group of lymphoproliferative disorders that account for 15% of all non-Hodgkin lymphomas (NHLs). The majority of these are peripheral T-cell lymphomas (PTCL). T-cell lymphomas are highly variable in their clinical presentation and prognosis. Research over the past few decades has revealed that these malignancies are biologically distinct with unique molecular, pathologic, and clinical features. This understanding has led to greater classification of T-cell lymphomas into separate subtypes. The identification of these malignancies as distinct entities is improving outcomes for patients with PTCL by enabling greater individualization of therapy and identifying new therapeutic targets.