Research to date suggests that individuals with headache may use experiential avoidance as a coping mechanism to manage pain or other private events (e.g. thoughts) related to their headache difficulties. Despite the wide use of avoidance in headache management, very little empirical evidence exists to support its effectiveness. Indeed, attempts at avoiding headache triggers or other internal private experiences associated with headache, may increase trigger potency, restrict lifestyle, decrease internal locus of control, and exacerbate and maintain pain perception. New treatment approaches, such as Acceptance and Commitment Therapy, emphasize acceptance and valued-living as alternatives to avoidance, have demonstrated to reduce headache-related disability and improve quality of life. Though APA has recently included ACT as an empirically supported treatment for chronic pain, very little evidence exists as to its effectiveness for head pain. The purpose of the present study is twofold. First, it examines, in a Randomized control study (RCT), how an ACT-based intervention for headache sufferers (added to medical treatment as usual-MTAU) improves quality of life and decreases disability. Second, it investigates whether the proposed process of change mechanism (i.e., acceptance and values-based actions) mediates headache interference and treatment outcomes (i.e. quality of life). It is expected that the ACT-based group in comparison to only MTAU group, will result in lower headache-related interference, higher emotional and physical functioning and increase in quality of life. Results of this study will offer new evidence regarding the utility of ACT in the management of primary headaches.