Apps for smart phones and tablets are also used for promotion of health behaviors, including promotion opf phyiscal activity. In May 2013, the iTunes and Google Play stores respectively contained 23,490 and 17,756 apps categorized as Health and Fitness, respectively. It is, however, unclear if these apps are of good enough quality to make a difference. In a paper just published in preliminary form in the International Journal of Behavioral Nutrition and Physical Activity -with Anouk Middelweerd as first author - we reviewed a selection of these apps on to what extend these apps made use of evidence-based, established behavior change techniques. Sixty-four apps were downloaded, reviewed, and rated based on the taxonomy of behavior change techniques used in the interventions as proposed by Abraham and Michie. Mean and ranges were calculated for the number of observed behavior change techniques. Using nonparametric tests, we compared the number of techniques observed in free and paid apps and in iTunes and Google Play.On average, the reviewed apps included 5 behavior change techniques (range 2-8). Techniques such as self-monitoring, providing feedback on performance, and goal-setting were used most frequently, whereas some techniques such as motivational interviewing, stress management, relapse prevention, self-talk, role models, and prompted barrier identification were not. No differences in the number of behavior change techniques between free and paid apps, or between the app stores were found. Our study demonstrated that apps promoting physical activity applied an average 5 out of 23 possible behavior change techniques. This number was not different for paid and free apps or between app stores. The most frequently used behavior change techniques in apps were similar to those most frequently used in other types of physical activity promotion interventions.