OBJECTIVES: The purpose of the literature review (Chapter 1) was to examine the literature on tailored mHealth interventions for physical activity (PA) in adults. The review demonstrated tailored mHealth programs were effective at promoting PA. Research was needed to test the impact of tailored materials over other types of materials. The purpose of the research study (Chapter 2) was to examine the impact of tailored versus targeted messages on participant non-compliance during Desire2Move (D2M; a health and well-being initiative promoting PA). METHODS: Eligible participants were D2M participants who were non-compliant (logged zero minutes during a program week) at least once. Departments were randomized into the “targeted message only” (TMO) or “targeted + tailored message” (TTM) group. Participants who did not provide a program goal were in the default control group (DC). After the first instance of non-compliance, participants received a targeted message. For subsequent instances of non-compliance, the TMO group continued to receive the same targeted message, up to three consecutive times. The TTM group received a message tailored to the participant’s program goal. The DC group did not receive additional messages. RESULTS: A total of 149 D2M participants were included for analysis. Participants were mostly female (68.5%), staff (44.3%), with an average age of 43.66 (SD = 11.10). Age, employee status, and PA status were controlled for in each model. A nested ANCOVA revealed a significant difference in non-compliance between the TTM (M = 2.64, SD = 1.93) and TMO (M = 3.95, SD = 2.1) groups, F(16,88) = 3.39, p < .001, η² = .38; d = .64. The ANCOVA that compared the TTM (M = 2.64, SD = 1.93) and DC (M = 3.75, SD = 2.10) groups revealed a significant difference, F(1,74) = 13.29, p < .001, η² = .152; d = .56. There was not a significant difference between the TMO and DC groups, F(1,80) = .10, p = .750, η² = .001; d = .02. CONCLUSION: Tailored email messages appeared to improve program implementation and are encouraged for future programs. Additional research is needed to understand how message frequency influences non-compliance and how PA status influences message effectiveness.