Young Lives research is particularly innovative in two areas: the measurement of mental health and the measurement of social capital, or social networks and support. Both of these areas pose particular challenges for researchers, and are of great interest to policymakers and planners. Thus, it is essential that methods and instruments used for measuring social capital and mental health be assessed for their efficacy. This paper examines the reliability of two instruments used by Young Lives researchers in Vietnam for measuring mental health and social capital respectively. In Part I: Validity and Reliability of the Self-Reporting Questionnaire in Vietnam, the authors discuss the methodology and results of a survey of child well-being in Vietnam that included measurements of maternal mental health. In Part II: Validity of a Social Capital Measurement Tool in Vietnam, the authors discuss the methodology and results of a survey on social capital in Vietnam. The authors detail the findings of both surveys, and present conclusions and recommendations for further research.