Despite the existence of evidence-based interventions for anxiety disorders, many barriers impede access to effective treatment services (e.g., distance from services, comorbidity). This dissertation aimed to investigate ways to overcome some of these barriers by exploring (1) the efficacy of therapist-supported distance cognitive behavior therapy (CBT) for anxiety disorders in adults, (2) the suitability of anxiety sensitivity (AS; a fear of arousal-related physiological sensations) as a target for transdiagnostic treatment, and (3) the efficacy of a distance CBT intervention for reducing high AS and its associated mental health and substance use symptoms. In Study 1, a systematic review showed that therapist-supported distance CBT was more efficacious than a waiting list and as efficacious as face-to-face CBT in reducing anxiety symptoms, increasing the likelihood of diagnostic remission, and improving quality of life. In Study 2, AS was associated with panic, posttraumatic stress, social phobia, and depressive symptoms. Of its lower order subscales, physical concerns predicted unique variance in panic, cognitive concerns predicted unique variance in depressive symptoms, and social phobia was predicted by social concerns. Together, Studies 1 and 2 suggest that distance CBT for anxiety is efficacious and that AS may be a suitable target for transdiagnostic interventions. As such, Studies 3 and 4 report on a randomized controlled trial investigating the efficacy and transdiagnostic implications of a telephone-delivered CBT intervention for high AS. The treatment significantly reduced AS relative to a waiting list and led to significant reductions in panic, posttraumatic stress, and social phobia symptoms (though not generalized anxiety or depressive symptoms). Treatment-related reductions in AS mediated these anxiety symptom changes. Participants in the treatment, vs. control, group also showed a significantly greater reduction in number of mental health diagnoses and in functional disability. Treatment also significantly reduced coping-with-anxiety drinking motives and physical alcohol-related problems for the treatment but not waiting list group. Reductions in AS mediated changes in coping-with-anxiety motives, while coping-with-anxiety motives mediated changes in physical alcohol-related problems. Taken together, findings from this dissertation provide evidence that distance-based and transdiagnostic AS-focused interventions may be two important and efficacious ways to overcome several barriers to anxiety treatment.