Objective: To examine the relationship between health belief model (HBM; i.e., perceived threat, benefits, costs, and self-efficacy) and theory of planned behavior (TPB; i.e., attitudes, social norms, and perceived behavioral control) constructs and parents' intention to participate and initial engagement (i.e., recruitment, enrollment, and first attendance) with a parenting intervention. Method: Participants were parents (n = 699, mean age = 38.29 years, 90.4% mothers) of 2-12-year-old children. The study conducted secondary analysis of cross-sectional data collected for an experimental study of engagement strategies. Participants provided self-report data on HBM constructs, TPB constructs, and intention to participate. Measures of initial parent engagement were also collected (i.e., recruitment, enrollment, and first attendance). Logistic regressions evaluated the impact of HBM and TPB constructs, and their combination, on intention to participate and initial parent engagement. Results: Analyses indicated that all HBM constructs increased the odds of parents' intention to participate and enrollment. In terms of TPB, parents' attitudes and subjective norms, but not perceived behavioral control, were significant predictors of intention to participate and enrollment. When combined in one model, parents' perceived costs, self-efficacy, attitudes, and subjective norms predicted intention to participate, whereas perceived threat, costs, attitudes, and subjective norms increased odds of enrolling in the intervention. Regression models for first attendance were not significant and those for recruitment could not be conducted due to lack of variance. Conclusions: The findings demonstrate the relevance of using both HBM and TPB constructs when enhancing parent intention to participate and enrollment. This document is copyrighted by the American Psychological Association or one of its allied publishers.This article is intended solely for the personal use of the individual user and is not to be disseminated broadly.Carolina Gonzalez https://orcid.org/0000-0002-8157-2056 Carolina Gonzalez was supported by a scholarship granted by Agencia Nacional de Investigacio ´n y Desarrollo (ANID) Becas Chile 72160251. The authors thank all parents around Australia who completed the survey. They also thank all the principals, directors, and staff from the childcare centers and schools across Australia, who shared this survey with parents. They would like to acknowledge the Departments of Education of New South Wales, Victoria, Northern Territory, South Australia, Tasmania, Queensland, and Australian Capital Territory, for allowing researchers to contact schools in their states/ territories. They also thank parent organizations for sharing this survey with parents within their organizations, that is, Australian Council of State School Organisations, Australian Parents Council, and Isolated Children's Parents' Association of Australia. They would also like to acknowledge Paul Jackson, who assisted with the setup of the online survey used ...