This clinical trial compares a novel smartphone application (app) called QuitQuest to the National Cancer Institute's (NCI's) SmokefreeTeenQuitVaping (SFTQV) app in helping teens stop vaping. Despite recent declines, data shows that 8.5% of middle school (grades 6-8) and 18.1% of high school (grades 9-12) students in the United States (US) used electronic nicotine delivery systems (ENDS; variously known as vaping, electronic \[e\]-cigarettes, e-cigs, mods, and tank systems that contain nicotine). Use of any tobacco product during adolescence increases risk for lifelong nicotine addiction. ENDS use, in particular, leads to severe asthma attacks, e-cigarette or vaping product use-associated lung injury (EVALI), exposure to multiple lung irritants, including volatile organic compounds, and lasting harm to adolescent brain development. Despite evidence of potential long-term harms from ENDS, to date there have been limited evidence-based therapeutic options for ENDS cessation for adolescents and young adults. Traditional methods for delivering adolescent ENDS cessation interventions (e.g., quitlines and clinics) have limited reach. QuitQuest utilizes Acceptance and Commitment Therapy (ACT), a psychological intervention that uses acceptance and mindfulness strategies, together with commitment and behavior change strategies, to increase psychological flexibility, reduce distress, and promote behavior change through mechanisms that include cultivating acceptance of internal experience and aligning behavior with personal values. The SFTQV program is based on the US Clinical Practice Guidelines, offering practical advice and support via an app delivery format. The QuitQuest app may work better than the SFTQV app in increasing vape quit rates among teens.