Recent research indicates that even 3.5-month-old infants are able to represent and to reason about the existence and properties of occluded objects. The presence of sophisticated physical reasoning at such a young age suggests that infants are born prepared to learn about physical events. Experiments on infants' reasoning about occlusion, support, and collision events suggest three hypotheses about infants' approach to the task of learning about the physical world. The first is that in their initial pass at understanding a class of physical events, infants build all-or-none, core representations that capture the essence of the events but few of the details. With further experience,e these core representations are progressively elaborated. Infants slowly identify the variables that are relevant to the events' outcomes, study their effects, and incorporate this accrued knowledge into their reasoning, resulting in increasing accurate predictions over time. The second hypothesis is that, once infants have identified variables as being relevant to events, they are able to reason first qualitatively and only later quantitatively about the effects of these variables. Finally, the third hypothesis is that, although infants' approach to learning about the physical world remains the same throughout infancy, what events are understood at what ages depends on a host of developmental factors including infant's visual, motoric, and representational abilities. The research proposed in this application will build on the three hypotheses just described. Five lines of research are planned. The first will focus on the distinction between core events and variables; some experiments will investigate further infants' understanding of the variables that affect support and collision events, while others will attempt to determine whether additional events also lend themselves to descriptions in terms of core events and variables. The second line of research will seek to shed further light on the distinction between infants' qualitative and quantitative physical reasoning. The third line of research will examine how representational factors affect the age at which infants come to understand different types of physical events. The fourth line of research will begin to examine the role of causality in infants' reasoning and learning about core events and variables. Finally, the fifth line of research will begin to explore the nature of the experiences that lead infants to identify core events and variables.