Psychotherapy was until recently described from a biological standpoint as causing structural changes in the brain and physiological alterations of neurotransmission pathways. Current research recognizes that psychotherapy also causes changes at the level of the DNA, with alterations in epigenetic mechanisms that correlate with symptom reduction and treatment response. The authors provide a brief overview of the evolving research in epigenetics, highlighting the association between trauma, DNA methylation patterns of specific gene regions, and psychiatric disorders. They also review several studies that show that various evidence-based psychotherapy interventions recalibrate these DNA methylation abnormalities. Finally, they identify studies that measured DNA methylation of BDNF and HTR3A genes and suggest that these may serve as biological markers of response to psychotherapy.