We integrate converging evidence from a variety of research areas in typical and atypical development to motivate a developmental framework for understanding the emergence of autism in infancy and to propose future directions for a recent area of research focusing on infant siblings of children with autism. Explaining the cognitive profile in autism is best achieved through tracing the process through which associated symptoms emerge over development. Understanding this process would shed light on the underlying causes of this multifaceted condition through clarifying how and why a variety of risk factors, single or in combination, exert an impact on the resulting phenotype. We emphasize the importance of integrating theoretical models of typical development in understanding atypical development and argue for the need to develop continuous and individually valid measures for at-risk infants both for predictors and outcomes of autism symptoms.