The purpose of this article is to synthesize the available studies regarding responsive interaction intervention (RII) for children with or at risk for developmental delays with a focus on six dimensions: (a) the characteristics of participants, (b) the features of RII, (c) the measurement of treatment fidelity, (d) the overall effectiveness of RII as reflected by the percentage of studies reporting significant changes in adult or child outcomes, (e) the measurement of maintenance and generalization of RII effects, and (f) the social validity or level of acceptability. Through a search of articles from 1990 to 2010, the authors identified 26 studies (31 articles) employing group experimental or quasiexperimental designs incorporating these dimensions. Overall, the results of the reviewed studies indicated that implementation of RII resulted in significant positive changes in adults' responsive behaviors and children's emotional and social-communicative outcomes. Although the most frequently reported child outcomes were in the social-communication domain, the most consistently significant positive outcomes for parent and child outcomes were in the emotional domain. The authors identify several gaps in this literature and suggest areas where research is needed. (Contains 2 tables and 2 figures.)