The idea of a "bipolar spectrum" is controversial due to 1) lack of widely accepted definitions, 2) concern that spectrum definitions might subsume cases with non-bipolar disorders, 3) worry that "diagnostic creep" may lead practitioners to overdiagnose bipolar disorder in marginal cases, and 4) worry that more diagnosis of bipolar spectrum may increase aggressive pharmacotherapy. These concerns are weighed against theoretical and empiric evidence converging in support of the bipolar spectrum as having prognostic and prescriptive validity. Practitioners can use inexpensive and practical strategies to incorporate the spectrum concept into their work while minimizing risks of overdiagnosis or unnecessary medication exposure.