This editorial introduces a series of articles that highlight the need for more research to address issues related to the implementation of treatments in routine settings. One of the themes highlighted by these papers is the importance of conceptual frameworks. Conceptual models guide the assessment process and provide the underlying logic model for different treatment programmes, but there is no agreed conceptual framework to guide the development of clinical decisions. A second theme raised by these papers is the importance of understanding the mechanisms underlying the development of mental health problems in young children, and the mediators and moderators of change. The third theme relates to the adoption of new assessment and treatment models. An awareness of issues related to implementation is important in facilitating the uptake of evidence-informed assessment and treatment models into routine clinical practice.