Infants master crawling and walking in an environment filled with varied and unfamiliar surfaces. At the same time, infants' bodies and skills continually change. The changing demands of everyday locomotion require infants to adapt locomotion to the properties of the terrain and to their own physical abilities. This Monograph examines how infants acquire adaptive locomotion in a novel task--going up and down slopes. Infants were tested longitudinally from their first week of crawling until several weeks after they began walking. Everyday locomotor experience played a central role in adaptive responding. Over weeks of crawling, infants' judgments became increasingly accurate, and exploration became increasingly efficient. There was no transfer over the transition from crawling to walking. Instead, infants learned, all over again, how to cope with slopes from an upright position. Findings indicate that learning generalized from everyday experience traveling over flat surfaces at home but that learning was specific to infants' typical method of locomotion and vantage point. Moreover, learning was not the result of simple associations between a particular locomotor response and a particular slope. Rather, infants learned to gauge their abilities on-line as they encountered each hill at the start of the trial. Change in locomotor responses and exploratory movements revealed a process of differentiation and selection spurred by changes in infants' everyday experience, body dimensions, and locomotor proficiency on flat ground.