ABSTRACT: BACKGROUND:Many Canadian adolescents and young adults with mental health problems face delayed detection, long waiting lists, poorly accessible services, care of inconsistent quality and abrupt or absent inter-service transitions. To address these issues, ACCESS Open Minds, a multi-stakeholder network, is implementing and systematically evaluating a transformation of mental health services for youth aged 11 to 25 at 14 sites across Canada. The transformation plan has five key foci: early identification, rapid access, appropriate care, the elimination of age-based transitions between services, and the engagement of youth and families. METHODS:The ACCESS Open Minds Research Protocol has multiple components including a minimum evaluation protocol and a stepped-wedge cluster randomized trial, that are detailed in this paper. Additional components include qualitative methods and cost-effectiveness analyses. The services transformation is being evaluated at all sites via a minimum evaluation protocol. Six sites are participating in the stepped-wedge trial whereby the intervention (a service transformation along the key foci) was rolled out in three waves, each commencing six months apart. Two sites, one high-population and one low-population, were randomly assigned to each of the three waves, i.e., randomization was stratified by population size. Our primary hypotheses pertain to increased referral numbers, and reduced wait times to initial assessment and to the commencement of appropriate care. Secondary hypotheses pertain to simplified pathways to care; improved clinical, functional and subjective outcomes; and increased satisfaction among youth and families. Quantitative measures addressing these hypotheses are being used to determine the effectiveness of the intervention. DISCUSSION:Data from our overall research strategy will help test the effectiveness of the ACCESS Open Minds transformation, refine it further, and inform its scale-up. The process by which our research strategy was developed has implications for the practice of research itself in that it highlights the need to actively engage all stakeholder groups and address unique considerations in designing evaluations of complex healthcare interventions in multiple, diverse contexts. Our approach will generate both concrete evidence and nuanced insights, including about the challenges of conducting research in real-world settings. More such innovative approaches are needed to advance youth mental health services research. TRIAL REGISTRATION NUMBER:Clinicaltrials.gov, ISRCTN23349893 (Retrospectively registered: 16/02/2017).