Purpose: A recent approach to identifying early markers of risk for autism spectrum disorder (ASD) has been to study infants who have an older sibling with ASD. These infants are at heightened risk (HR) for ASD and for other developmental difficulties, and even those who do not receive an eventual ASD diagnosis manifest a high degree of variability in trajectories of development. The primary goal of this review is to summarize findings from research on early motor and communicative development in these HR infants. Method: This review focuses on 2 lines of inquiry. The first assesses whether delays and atypicalities in early motor abilities and in the development of early communication provide an index of eventual ASD diagnosis. The second asks whether such delays also influence infants' interactions with objects and people in ways that exert far-reaching, cascading effects on development. Results: HR infants who do and who do not receive a diagnosis of ASD vary widely in motor and communicative development. In addition, variation in infant motor and communicative development appears to have cascading effects on development, both on the emergence of behavior in other domains and on the broader learning environment. Conclusions: Advances in communicative and language development are supported by advances in motor skill. When these advances are slowed and/or when new skills are not consolidated and remain challenging for the infant, the enhanced potential for exploration afforded by new abilities and the concomitant increase in opportunities for learning are reduced. Improving our understanding of communicative delays of the sort observed in ASD and developing effective intervention methods requires going beyond the individual to consider the constant, complex interplay between developing communicators and their environments. [This article stems from the 2017 Research Symposium at American Speech-Language-Hearing Association (ASHA) Convention.]