This document summarizes research on the genetics and pharmacogenetics of mood disorders. It discusses how genome-wide association studies have identified several genes linked to bipolar disorder and major depressive disorder. Specifically, the CACNA1C gene was found to be strongly associated with bipolar disorder. Variations in genes involved in neuroplasticity and inflammation may help explain individual differences in risk. Pharmacogenetic research has also found genetic factors influence patients' responses to antidepressants by impacting drug metabolism and target receptors in the brain. Understanding a patient's genetic profile could someday help clinicians personalize treatment selection and dosing.