Increased interest in early life origins of chronic disease, a concept often referred to as programming, has resulted in several studies investigating the origins of childhood or adulthood obesity during infancy. Rapid infancy weight gain as a risk factor and breastfeeding as a protective factor for later obesity have been most thoroughly studied. The association between rapid infancy weight gain and later obesity is supported by several observational studies, but not by the two, relatively small, randomized trials. This association is strong, suggests a dose-response effect and has biological plausibility, but is not consistent between study designs. Rapid infancy weight gain as a risk factor for later obesity has been experimentally reproduced in animal models, but not in humans. The protective effect of breastfeeding on obesity is also supported by several observational studies, but randomized trials are not available. Considering the potential for residual confounding factors, current evidence is insufficient to demonstrate origins of obesity during infancy or to change public health recommendations, but the potential for obesity prevention during infancy is promising.