This synthesis has been developed to describe early childhood mental health consultation (ECMHC) and the existing evidence base for its effectiveness in fostering healthy social and emotional development in young children, birth through age 6. It provides a description of the emerging evidence base that many of the beliefs and much of the current body of knowledge about consultation is grounded in literature and the experiences of mental health and early care and education (ECE) providers, educators, and other experts (i.e., practice-based evidence). Most empirical research focuses on the impact of consultation on child, program, staff and, to a lesser extent, family outcomes. Still, research efforts are occurring and data to support ECMHC as an effective model for service delivery are accumulating. (author abstract)