The past two decades have yielded an exponential increase in research exam-ining the genetic and environmental factors that affect individual differences in mood regulation and increase susceptibility to bipolar disorder (BD) and other mood disorders. This rapid accumulation of new knowledge has demonstrated the potential impact of behavioral and molecular genetic methods. However, the complicated and sometimes contradictory results that have emerged from these studies also illustrate the complexity of the etiological pathways to BD and under-score how much remains to be learned. E Willcutt, M McQueen Journal Article