Patients with obsessive compulsive disorder (OCD) often experience aversive emotions in response to obsessions, which motivate them to engage in compulsive behaviors. Moreover, OCD patients show pronounced emotion regulation (ER) deficits, which may be critical for OCD severity. However, little is known about the neurobiology of ER in OCD and how the modulation of these processes contributes to symptoms’ improvement. Here, we propose to characterize these patients with a comprehensive clinical and neuroimaging assessment, focusing on basic psychological processes related and on the neurobiological underpinnings of ER. After a baseline assessment, we aim to assess the efficacy of an internet-based psychotherapy intervention protocol, combining cognitive-behavioral therapy and third-wave interventions (mindfulness and acceptance and commitment therapy) on the modulation of ER and OCD severity. Specifically, we will (1) examine to what extent the psychotherapeutic intervention modulates ER and the associated neurobiological mechanisms and (2) identify candidate biomarkers of successful treatment response.