The social cognition and perception-action literatures are largely separate, both conceptually and empirically. However, both areas of research emphasize infants' emerging abilities to use available information-social and perceptual information, respectively-for making decisions about action. Borrowing methods from both research traditions, this study examined whether 18-month-old infants incorporate both social and perceptual information in their motor decisions. The infants' task was to determine whether to walk down slopes of varying risk levels as their mothers encouraged or discouraged walking. First, a psychophysical procedure was used to determine slopes that were safe, borderline, and risky for individual infants. Next, during a series of test trials, infants received mothers' advice about whether to walk. Infants used social information selectively: They ignored encouraging advice to walk down risky slopes and discouraging advice to avoid safe slopes, but they deferred to mothers' advice at borderline slopes. Findings indicate that 18-month-old infants correctly weigh competing sources of information when making decisions about motor action and that they rely on social information only when perceptual information is inadequate or uncertain. Two sources of information are available to infants for making decisions about action: perceptual information generated by infants' own exploratory movements and social information offered by infants' parents and other people. An eager infant poised at the top of the stairs as mother screams "No!," a timid infant who is encouraged to attempt the daunting playground slide, a crawling infant whose parent's silence conveys that it is okay to roam, and a beginning walker reluctant to take steps into mother's open arms must decide whether to descend, slide, crawl, and walk on the basis of the available perceptual and social information.Sometimes perceptual and social cues are concordant, offering redundant information that specifies the way to act (e.g., when parents nod toward an inviting toy or say "No, no" toward a menacing dog). Other times, perceptual and social information are at odds, specifying opposing courses of action (e.g., when parents warn their toddlers to stay away from an empty street or encourage their infants to crawl onto the unfamiliar surface of a sandy beach). Discordant perceptual and social information is especially interesting because infants confront an interpretive challenge: They must decide how to weigh and integrate competing sources of information. In such situations, infants might assign priority to social information and defer to mothers' advice, regardless of their own perceptual assessment of the situation. Alternatively, infants might rely on perceptual information and ignore their mothers' social messages. A third possibility is that infants assess social and perceptual cues on a case-by-case basis, relying selectively on social information when perceptual cues leave them uncertain about how to act. On this last account, infan...