Cigarette smoking is the leading cause of mortality in the U.S., resulting in over 480,000 deaths every year and costing $278 billion in loss of productivity. Smoking is also the leading cause of cancer and of deaths from cancer. Smoking causes cancers of the lung, larynx, mouth, bladder, liver, kidney, colon, rectum and others. While smoking rates in the U.S. have declined over recent years, continued smoking is strongly associated with both depressive disorders and depressive symptoms, with smoking rates remaining at 30-50% among individuals with depressive disorders. Depressive symptoms have also been shown to predict smoking cessation failure. While clinical practice guidelines for nicotine dependence treatment suggest the need to address psychological issues such as elevated depressive symptoms, empirically validated interventions to address this important risk factor are lacking. Tobacco quitlines are the major vehicle through which smoking cessation services are delivered in the U.S and are available in every U.S. state via a national quitline portal, 1-800-QUIT-NOW. However tobacco quitlines, as they currently exist, deliver standard behavioral smoking cessation treatment and are not well equipped to effectively help smokers with conditions such as comorbid depression. Indeed, a recent study reported that 24% of smokers calling a state tobacco quitline had a significantly elevated level of depressive symptoms and that these smokers with depressive symptoms, compared to those without, were significantly less likely to successfully quit smoking. Tobacco quitlines would derive significant benefit from an adjunctive psychosocial approach to address the depressive symptoms experienced by many of their clients. While issues of feasibility limit the use of such approaches in a standard delivery method, their use in the form of a mobile application (app) holds significant promise. Behavioral Activation is an empirically supported treatment that is straightforward, easily understood, and as such is particularly amenable to a mobile platform and to systematic integration with tobacco quitline counseling. Across studies, Behavioral Activation is effective for reducing depressive symptoms among individuals with sub threshold depression as well as individuals with major depressive disorder (MDD) and it meets the criteria to be established as an empirically supported treatment. The aims of this Phase I application are to employ user centered design processes to develop and test the acceptability and efficacy of a mobile health app, Act2BSmokeFree, which will incorporate brief Behavioral Activation vs. a relaxation app, Breathe2Relax in a small randomized controlled trial of smokers with elevated depressive symptoms. All participants will receive tobacco quitline counseling. The expected outcome of this project is the development of a prototype of Act2BSmokeFree, which can readied for Phase II testing of clinical efficacy in a future randomized controlled trial in conjunction with tobacco quitline counseling.