New studies of early intervention effects in ASD are being published monthly, with varying designs, methods, measures, and outcomes. There is growing acceptance of the ideas that (1) individual outcomes in autism reflect transactional processes among environmental and biological variables throughout life and (2) that developmental processes and rates may be particularly malleable in early childhood. There is increasing impetus among families and care professionals for early intervention research findings to be incorporated into an increased range, sophistication, and availability of services to young children and their families. However, this impetus is tempered by concerns about overemphasis on early childhood services, unreliability of early symptoms, difficulties with assessment processes, and lack of community services for early identification, diagnosis, and treatment. In order to guide public services and clinical practice, early intervention science must move more deeply into two areas (among many): (1) mechanisms by which specific intervention practices may be changing children's developmental trajectories or rates, (2) individual or subgroup patterns of response to specific interventions, and (3) variables that mediate and moderate intervention response. This international panel brings together a distinguished group of scientists involved in studying the processes and mechanisms involved in response to early interventions.