 This research examined the use of health-related mobile phone apps by US mobile phone users. It found that 58% of participants had downloaded a health-related app, with fitness and nutrition being the most popular categories. Younger, wealthier, and more educated people were more likely to download these apps. Additionally, cost was a major barrier to app adoption, with many respondents stating that they would not pay for any health apps. Most participants also reported that the apps had improved their health, but a majority of those who had downloaded the apps eventually stopped using them due to high data entry burdens or loss of interest. This suggests that app developers should focus on addressing consumer concerns, such as cost and data entry burden, and conduct clinical trials to test the efficacy of health apps. This article was authored by Krebs, Paul, and Duncan, Dustin T.