Research on the effectiveness of early intervention with handicapped children is reviewed in this information digest. Presented in question and answer format, the digest addresses the following questions: What is early intervention? Why intervene early? Is early intervention really effective? Is early intervention cost effective? Are there critical features to include in early intervention? It is concluded that both quantitative and qualitative data indicate that early intervention increases the developmental/educational gains for the child resulting in (1) his needing few special education and other habilitative services later in life; (2) being retained in grade less often; and (3) in some cases being indistinguishable from nonhandicapped classmates years after intervention. Long term cost effectiveness is also supported by the data. Characteristics of successful early intervention programs include intervening when the child is as young as possible, involving parents in the child's treatment, and structuring the program to precisely identify child and family objectives and teaching behaviors. (DB)