Forty percent of obsessive-compulsive disorder (OCD) patients fail to respond to any kind of treatment. Developing novel therapies for OCD—the aim of this thesis—therefore represents an urgent unmet need. Study 1 examined vicarious contamination sensations and relief in OCD. Study 2 explored the therapeutic utility of the “rubber hand illusion” (RHI) and multisensory processing in OCD. Study 3 tested two novel smartphone interventions in subclinical OCD. In Study 1, OCD patients (n = 29) reported greater contamination sensations when watching the experimenter contaminating himself than healthy volunteers (n = 34). But more notably, patients, upon first contaminating themselves, reported significant disgust reductions by watching the experimenter washing his own hands, relative to control conditions (unlike anxiety and washing urges); and displayed a (nonsignificant) tendency towards disgust reductions during vicarious handwashing relative to control conditions, compared to healthy volunteers. Finally, an exploratory analysis found that patients with moderate symptoms, unlike severe patients, reported greater reductions in disgust and handwashing urges from vicarious handwashing relative to control conditions, compared to healthy controls. In Study 2, in patients with OCD (n = 27) “dummy contamination” during the RHI resulted in greater contamination reactions than the control (contrary to expectations, after the fake hand had been contaminated for 5 min.); assessed via disgust facial expressions and in vivo exposure. Surprisingly, patients failed to reject the RHI during the “gold-standard” control condition. In Study 3, subclinical individuals (n = 93) either watched a video recording of themselves: engaging in handwashing (intervention 1), touching a disgust-inducing object (intervention 2), or performing sequential hand movements (control), on a smartphone four times a day, for one week. As hypothesized, the two interventions, unlike the control, improved OCD symptoms and cognitive flexibility. These studies demonstrate, for the first time, vicarious contamination sensations and relief in OCD; suggest sensory assimilation of contamination sensations into the body image via the RHI and show aberrant self-referential processing in OCD. Finally, two novel smartphone interventions improved OCD symptoms and cognitive function, after only one week in subclinical individuals. Taken together, these results have important clinical implications for the treatment of OCD.