Background Digitally enabled care along with an emphasis on self-management of health is steadily growing. Mobile health apps provide a promising means of supporting health behavior change; however, engagement with them is often poor and evidence of their impact on health outcomes is lacking. As engagement is a key prerequisite to health behavior change, it is essential to understand how engagement with mobile health apps and their target health behaviors can be better supported. Although the importance of engagement is emphasized strongly in the literature, the understanding of how different components of engagement are associated with specific techniques that aim to change behaviors is lacking. Objective The purpose of this systematic review protocol is to provide a synthesis of the associations between various behavior change techniques (BCTs) and the different components and measures of engagement with mobile health apps. Methods The review protocol was structured using the PRISMA-P (Preferred Reporting Items for Systematic Reviews and Meta-Analyses Protocols) and the PICOS (Population, Intervention, Comparator, Outcome, and Study type) frameworks. The following seven databases will be systematically searched: PubMed, Embase, Cumulative Index to Nursing and Allied Health Literature, APA PsycInfo, ScienceDirect, Cochrane Library, and Web of Science. Title and abstract screening, full-text review, and data extraction will be conducted by 2 independent reviewers. Data will be extracted into a predetermined form, any disagreements in screening or data extraction will be discussed, and a third reviewer will be consulted if consensus cannot be reached. Risk of bias will be assessed using the Cochrane Collaboration Risk of Bias 2 and the Risk Of Bias In Non-Randomized Studies - of Interventions (ROBINS-I) tools; descriptive and thematic analyses will be conducted to summarize the relationships between BCTs and the different components of engagement. Results The systematic review has not yet started. It is expected to be completed and submitted for publication by May 2022. Conclusions This systematic review will summarize the associations between different BCTs and various components and measures of engagement with mobile health apps. This will help identify areas where further research is needed to examine BCTs that could potentially support effective engagement and help inform the design and evaluation of future mobile health apps. Trial Registration PROSPERO CRD42022312596; https://tinyurl.com/nhzp8223 International Registered Report Identifier (IRRID) PRR1-10.2196/35172

BACKGROUND The use of digitally-enabled care and the emphasis on self-management of health is growing. Mobile health apps provide a promising means of supporting health behaviour change; however, engagement with them is often poor and evidence of their impact on health outcomes is lacking. As engagement is a key prerequisite to health behaviour change, it is essential to understand how engagement with mobile health apps and their target health behaviours can be better supported. Despite an increasing recognition of the importance of engagement in the literature, there is still a lack of understanding of how different components of engagement are associated with specific techniques that aim to change behaviours. OBJECTIVE The purpose of this systematic review protocol is to provide a synthesis of the associations between various Behaviour Change Techniques (BCTs)and the different components of engagement (and their outcome measures) with mobile health apps. METHODS The review protocol was structured using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses Protocols (PRISMA-P) and the Population, Intervention, Comparator, and Outcome (PICO) frameworks. Six databases will be systematically searched: PubMed, Embase, Cumulative Index to Nursing and Allied Health Literature (CINAHL), APA PsycInfo, ScienceDirect, and Web of Science. Title and abstract screening, full-text review, and data extraction will be conducted by two independent reviewers. Data will be extracted into a predetermined form, and any disagreements in screening or data extraction will be discussed, with a third reviewer consulted if consensus cannot be reached. Risk of bias will be assessed using the Cochrane Collaboration Risk of Bias 2 and ROBINS-I tools and descriptive and thematic analyses will be used to summarise the relationships between BCTs and the different components of engagement. RESULTS The systematic review has not been started. It is expected to be completed and submitted for publication by January 2022. CONCLUSIONS This systematic review will summarize the associations between different BCTs and various components and measures of engagement with mobile health apps. This will identify areas where further research is needed to examine BCTs that could potentially support effective engagement and help to inform the design and evaluation of future mobile health apps. CLINICALTRIAL PROSPERO (reference number TBD)