This chapter reviews bipolar spectrum disorders (bipolar I, bipolar II, bipolar disorder not otherwise specified, and cyclothymic disorder) in childhood and adolescence. The history of the diagnosis in youth, including recent increased public and professional interest, and surrounding controversy is reviewed. Attention is given to prevalence, incidence, similarities and differences in presentation, course, and comorbidities among child, adolescent, and adult bipolar spectrum disorders. Assessment issues are reviewed, including longitudinal and multiinformant perspectives, instruments, strategies, tools, and assessment challenges with youth. Examples of symptom manifestation in youth are provided. Genetic, cognitive, neuroanatomical, psychosocial, and environmental risks for youth bipolar spectrum disorders are discussed. Evidence-based treatments reviewed include commonly prescribed mood stabilizers and atypical antipsychotics, alternative biological treatments, adjunctive psychotherapies, and complementary and alternative treatments. Finally, future directions for the study, assessment, monitoring, and treatment of youth bipolar spectrum disorders are discussed.