This evidence base update examines the level of empirical support for interventions for children with autism spectrum disorder (ASD) younger than 5 years old. It focuses on research published since a previous review in this journal (Rogers & Vismara, 2008). We identified psychological or behavioral interventions that had been manualized and evaluated in either (a) experimental or quasi-experimental group studies or (b) systematic reviews of single-subject studies. We extracted data from all studies that met these criteria and were published after the previous review. Interventions were categorized across two dimensions. First, primary theoretical principles included applied behavior analysis (ABA), developmental social-pragmatic (DSP), or both. Second, practice elements included scope (comprehensive or focused), modality (individual intervention with the child, parent training, or classrooms), and intervention targets (e.g., spoken language or alternative and augmentative communication). We classified two interventions as well-established (individual, comprehensive ABA and teacher-implemented, focused ABA þ DSP), 3 as probably efficacious (individual, focused ABA for augmentative and alternative communication; individual, focused ABA þ DSP; and focused DSP parent training), and 5 as possibly efficacious (individual, comprehensive ABA þ DSP; comprehensive ABA classrooms; focused ABA for spoken communication; focused ABA parent training; and teacher-implemented, focused DSP). The evidence base for ASD interventions has grown substantially since 2008. An increasing number of interventions have some empirical support; others are emerging as potentially efficacious. Priorities for future research include improving outcome measures, developing interventions for understudied ASD symptoms (e.g., repetitive behaviors), pinpointing mechanisms of action in interventions, and adapting interventions for implementation with fidelity by community providers.Autism spectrum disorder (ASD) is defined by difficulties with reciprocal social communication and stereotyped interests or behaviors (American Psychiatric Association [APA], 2013) that usually emerge in early childhood. About one third of children with ASD have delays in cognitive development and daily living skills (Autism and Developmental Disabilities Monitoring Network, 2014). Co-occurring behavior problems (tantrums, aggression, self-injury, impulsivity, anxiety, extreme food selectivity, insomnia) and medical conditions (e.g., seizure disorder, gastrointestinal disturbance) are also common. Although ASD almost always persists across the lifespan, early intervention can alleviate symptoms (Rogers & Vismara, 2008).ASD has a prenatal origin related to genetic risk and environmental events; however, the precise etiology has not been determined (Volkmar, Paul, Rogers, & Pelphrey, 2014). Although once considered rare, ASD is now estimated to occur in approximately 1 in 68 individuals (Autism and Developmental Disabilities Monitoring Network, 2014). It remains unknown whethe...