Currently, there are at least 400 smartphone apps for smoking cessation available (5,6). Smoking cessation apps are downloaded an average of 780,000 times per month (5).Despite their popularity, no prior studies have examined use of specific features of smoking cessation apps and whether this use predicted quitting. This type of analysis is a critical first step toward identifying the active ingredients of smartphone apps for smoking cessation and understanding whether users are being adequately exposed to these active ingredients.Although this has not been tested with smartphone apps, prior research has demonstrated a discrepancy between the features of a technology-delivered intervention that are most popular with users and those that are predictive of outcome. For example, a recent study of the BecomeAnEX.org website showed that the site’s cigarette tracker, quit plan, and tool for coping with smoking triggers were three of the most highlyaccessed features on the site, yet none were significantly predictive of 30-day abstinence