Objective: To describe the study design of Young Minds Matter: The second Australian Child and Adolescent Survey of Mental Health and Wellbeing. The aims of the study, sample design, development of survey content, field procedures and final questionnaires are detailed. Method: During 2013-2014, a national household survey of the mental health and wellbeing of young people was conducted involving a sample of 6310 families selected at random from across Australia. The survey included a face-to-face diagnostic interview with parents/carers of 4- to 17-year-olds and a self-report questionnaire completed by young people aged 11-17 years. Results: The overall response rate to the survey was 55% with 6310 parents/carers of eligible households participating in the survey. In addition, 2967 or 89% of young people aged 11-17 years in these participating households completed a questionnaire. The survey sample was found to be broadly representative of the Australian population on major demographic characteristics when compared with data from the Census of Population and Housing. However, adjustments were made for an over-representation of younger children aged 4 to 7 years and also families with more than one eligible child in the household. Conclusion: Young Minds Matter provides updated national prevalence estimates of common child and adolescent mental disorders, describes patterns of service use and will help to guide future decisions in the development of policy and provision of mental health services for children and adolescents. Advancements in interviewing methodology, addition of a data linkage component and informed content development contributed to improved breadth and quality of the data collected.