Physical inactivity is a key risk factor for a range of chronic diseases and conditions, yet, approximately 50% of U.S. adults fall below recommended levels of regular aerobic physical activity (PA). This is particularly true for ethnic minority populations such as Latino adults for whom few culturally adapted programs have been developed and tested. Text messaging (SMS) represents a convenient and accessible communication channel for delivering targeted PA information and support, but has not been rigorously evaluated against standard telehealth advising programs. The objective of the On The Move randomized controlled trial is to test the effectiveness of a linguistically and culturally targeted SMS PA intervention (SMS PA Advisor) versus two comparison conditions: a) a standard, staff-delivered phone PA intervention (Telephone PA Advisor) and b) an attention-control arm consisting of a culturally targeted SMS intervention to promote a healthy diet (SMS Nutrition Advisor). The study sample (N = 350) consists of generally healthy, insufficiently active Latino adults ages 35 years and older living in five northern California counties. Study assessments occur at baseline, 6, and 12 months, with a subset of participants completing 18-month assessments. The primary outcome is 12-month change in walking, and secondary outcomes include other forms of PA, assessed via validated self-report measures and supported by accelerometry, and physical function and well-being variables. Potential mediators and moderators of intervention success will be explored to better determine which subgroups do best with which type of intervention. Here we present the study design and methods, including recruitment strategies and yields. Trial Registration: clinicaltrial.gov Identifier = NCT02385591.