Background: Although Aboriginal peoples account for 2.5 percent of the overall population, they are disproportionately represented in statistics related to the utilisation of mental health services, hospital separation for injury and self-harm, and incarceration. To date, no systematic reviews of Aboriginal social and emotional wellbeing (SEWB) provide decision-makers in the Aboriginal community-controlled and government sectors with culturally applicable and transferable advice on what works, for whom and in what circumstances. Objective: To distil from programs on the prevention of mental health difficulties and promotion of SEWB among Aboriginal children and youth the relationships between context, mechanisms and outcomes. Method and Results: This realist review was based on the following priority areas identified in Australian policy documents and by policy-makers: crime and violence, substance misuse, adverse mental health, cultural pride, strengthening families, strengthening communities and education. A systematic search of academic databases and the grey literature retrieved 46 Australian programs implemented from 1998–2008 for which program processes or impact information was reported in relation to Aboriginal children and youth SEWB. Social identity theory and the cultural respect framework were ‘candidate theories’ that informed propositions in the initial theoretical framework. From testing these propositions and assessing evidence for ‘‘fitness of purpose’’, engaging participants emerged as a universal pathway that cut across all program types. Contextual factors associated with participant recruitment, engagement and attrition will be discussed in relation to program impacts and outcomes and specific mechanisms operating within the engagement pathway. ‘‘Best bets’’ identified by policy makers in South Australia will be presented. Conclusions: History, time in addition to factors related to the implementing community, sponsoring organisation, inter-agency collaboration and the workforce emerged as powerful influencers of engagement. This review finds that ‘‘upstream’’ investments need to be made to establish and maintain participant engagement in order for programs to impact SEWB.