This chapter reviews some of the key considerations of pharmacogenetics in the treatment of mood disorders. There have been a number of small studies aimed at finding genetic markers of antidepressant treatment outcome. If the serotonin transporter (SLC6A4) is the most studied gene in psychiatry, a functional polymorphism in its promoter region (known as the linked polymorphic region (LPR)), is the most studied genetic marker. Variation in brain-derived neurotrophic factor (BDNF) has been thought to play a role in the etiology of affective disorders and the mediation of antidepressant treatment response. Genome-wide association studies (GWAS) are a relatively new kind of genetic study that take advantage of large numbers of highly informative genetic markers, spread across each chromosome. Adverse events occur with all pharmacological treatments. Two groups of antidepressant-associated adverse events have been studied in large samples: treatment-emergent suicidal ideation (TESI) and sexual dysfunction (SD).