<p>Preventive parenting programs effectively promote positive parenting behaviors and prevent negative child behavioral health outcomes, but engagement is often low. Self-directed eHealth interventions are increasingly available as an option that offers flexibility and increased access for parents. Yet, reports of and operationalizations of engagement within self-directed programs vary and correlates of eHealth engagement are not well understood. Thus, this study systematically reviewed reports to identify common operationalizations of engagement in self-directed preventive eHealth parenting programs, predictors of engagement, and associations between engagement and child behavioral health outcomes. Of 835 records screened, 31 unique studies had caregivers that participated in a self-directed eHealth preventive parenting programs that defined engagement or program adherence. Most studies reported the number of modules completed as a measure of parent engagement. About one-third of programs also reported frequency of parent program access. There was great variability in variables examined as correlates of eHealth program engagement, limiting the ability to draw consistent patterns of predictors of engagement. Evidence linking engagement to youth mental and behavioral health outcomes was similarly limited. Although module or session completion was the most common metric, studies varied in how engagement was further defined and applied. This heterogeneity poses challenges for comparing engagement rates across studies, but individual studies provide emerging evidence of potential ways to increase engagement within self-directed programs (e.g., phone coaching, ordering of content). Overall, this review underscores the need for further research as eHealth interventions continue to be offered to parents.</p>