Hairy cell leukemia is an indolent B-cell non-Hodgkin's lymphoma with a characteristic presentation of pancytopenia, splenomegaly, and circulating hairy cells. An immunophenotypic pattern of CD11c, CD25, and CD103 expression. TRAP staining, reticulin deposition, and morphology of bone marrow and circulating cells help establish the diagnosis. Although up to 10% of patients might not require systemic treatment, for the vast majority effective treatments are available with the purine-nucleoside analogues cladribine and pentostatin. Cladribine is considered the drug of choice in the first-line setting due to the very high complete remission rate and prolonged duration of response following a single 7-day infusion. Cladribine and pentostatin both have unique but different mechanisms of action, with a lack of cross-resistance between them, which might be exploited in the relapsed or refractory disease setting. Therapy for relapsed and refractory patients also includes novel biologic agents as well as splenectomy. Despite the effective treatment options, the prospect of cure remains elusive due to the frequent presence of MRD even in complete responders. Future studies employing combination therapies targeting the eradication of MRD will hopefully improve relapse-free survivals as well as overall survival, and might even offer the prospect of cure.