Background: Research suggests family-based programs for the prevention and control of childhood obesity can significantly reduce child body mass index and increase healthy behaviors; yet, low parent engagement frequently hinders the implementation of these programs. This dissertation examined factors affecting parent engagement in a family-based childhood obesity prevention and control program conducted in Imperial County, CA. Methods: This dissertation study was ancillary to a multi-sector, multi-component childhood obesity prevention and control demonstration study named Our Choice, Nuestra Opcion. The ancillary study used a prospective, mixed-methods approach to examine parent engagement in one component of Our Choice, a Family Wellness Program which included 9 healthy lifestyle workshops and 8 physical activity workshops led by community health workers. Self-report surveys were administered to 128 parents assigned to the Family Wellness program at baseline, or prior to the start of intervention activities. The survey assessed hypothesized predictors of engagement including readiness to change, perceived relevance of the intervention, and family functioning. Anthropometric data (height and weight) and sociodemographic characteristics of both the parent and child were also collected at baseline. Attendance was recorded throughout the duration of the Family Wellness Program. A sub-set of parents (n=22) were interviewed following the scheduled completion of the Family Wellness program to assess their experiences in the program and to identify factors that influenced their level of engagement. Results: Results of quantitative analyses indicate parents' readiness to change their own health behaviors and their weight-related parenting strategies was the strongest predictor of their engagement in the Family Wellness Program. Child behavioral health issues also played a role in parent engagement. Qualitative analysis of interview data showed that parent engagement may also be influenced by the level of support and enthusiasm received from the participating child. Conclusions: This study elucidated the experiences of parents enrolled in familybased childhood obesity prevention and control programs. Results indicate that engagement may be improved by targeting parents' readiness to make changes during recruitment and early in the intervention. Also, parent engagement may be improved by implementing strategies to improve the participating child's attitudes towards the program. Overall, this dissertation has identified several potentially modifiable influences on engagement.