Bipolar disorder (BD) is a chronic, recurrent disorder carrying high morbidity and mortality, leading to health costs of at least $45 billion per year (Kleinman et al., 2003). It is the sixth leading cause of disability among all illnesses (Murray & Lopez, 1996). Between 15 and 28% of bipolar adults experience illness onset before the age of 13, and between 50 and 66% of them experience it before the age of 19 (Leverich et al., 2002, 2003; Perlis et al., 2004). The exact prevalence in children is unknown, but an estimated 420,000–2,072,000 US children have the illness (Post & Kowatch, 2006). Persons with onset of BD in childhood or adolescence have a more severe, adverse, and continuously cycling course of illness than adults, often with a preponderance of mixed episodes, psychosis, suicidal ideation or behaviors, and multiple comorbidities (Geller et al., 2002). Without early intervention, early-onset BD patients can be derailed, sometimes irrevocably, in social, neurobiological, cognitive, and emotional development (Miklowitz et al., 2004).Our work on this Special Issue and editorial was partially supported by grants from the National Institute of Drug Abuse, the National Institute of Mental Health, and the Spunk Fund, Inc.