This article reviews the current evidence base for the effectiveness of early childhood mental health consultation (ECMHC). Comprehensive program evaluations of ECMHC include a number of elements such as a theory of change, a defined program logic model, and tools to measure outcomes at multiple levels: child, teacher, classroom, program, and family levels. Seven statewide programs with strong program evaluations illustrate current research efforts and contributions to the evidence base. (author abstract)