Latina adolescents report low levels of physical activity, with only 3% meeting national physical activity guidelines, and are at high lifetime risk for conditions related to inactivity, such as obesity, metabolic syndrome, and diabetes. Interventions grounded in sound psychosocial theory and leveraging growing technology use in Latina adolescents are needed to reverse patterns of inactivity, establish healthy lifetime habits and reduce widening disparities. The research team has developed and tested individually tailored, culturally adapted web-based interventions to increase moderate-to-vigorous physical activity (MVPA) for Latinos, which significantly increased MVPA in adult Latino men and women. In a recent pilot study (R03NR014329), this intervention was adapted based on formative interviews to make it appropriate for Latina adolescents and tested it in a single-arm pilot trial (N=21). After 12 weeks, retention was high (90.5%) and self-reported MVPA increased from 24.7(26.11) minutes/week at baseline to 79.4(46.8) at follow up (p\<0.001), suggesting good potential efficacy. In closeout interviews, girls expressed a preference to increase audiovideo components of the website and to incorporate other mobile-health technologies, such as texting, smartphone apps, social media, and wearables. Thus, the aim of this study is to conduct a randomized controlled trial (N=200) of an individually tailored, theory-based, multi-technology intervention to increase MVPA in Latina adolescents. The intervention will comprise a counseling session to teach behavior change techniques, an interactive multimedia website with individually tailored content based on principles of the Transtheoretical Model and Social Cognitive Theory, a wearable tracker and smartphone app to reinforce key behavior change techniques, connection with a study Instagram account to reinforce exposure to intervention content, and automated text messages guide continued goal setting. Participants will be randomly assigned to receive the intervention or only a wearable tracker with smartphone app. Activity will be measured at baseline and six-month follow-up using well-established MVPA measures (accelerometers and the 7-Day Physical Activity Recall Interview). It is hypothesized that those randomized to receive the intervention will show significantly greater increases in MVPA at six months than those in the control group. The investigators will also evaluate whether changes in MVPA are mediated by changes in targeted psychosocial constructs (e.g. self-efficacy, social support) or engagement with technology, assess longer-term changes in MVPA at 12 months, and evaluate whether intervention effects are moderated by baseline personal and environmental variables (e.g. age, BMI, neighborhood environment). Costs to deliver the intervention (e.g. staff time, materials, overhead) will be tracked to evaluate costs and cost-effectiveness of both study arms, and the investigators will track contact time to assess whether staff contact is related to study outcomes. The investigators will also explore trajectories of daily activity in both the intervention and control groups using continuous data from wearable trackers. The proposed study will promote a critical preventive health behavior, physical activity, in Latina adolescents using technologies that are pervasive in this high risk, quickly growing population and highly scalable, laying the groundwork for cost-effective, broad reaching interventions with great potential for preventing chronic disease and promoting health and wellbeing throughout the lifespan.