Three experiments document that conceptual knowledge influences lexical acquisition in infancy. A novel target object was initially labeled with a novel word. In both yes-no (Experiment 1) and forced-choice (Experiment 2) tasks, 2-year-olds' subsequent extensions were mediated by the conceptual description of the targets. When targets were described as artifacts, infants extended on the basis of shape. When targets were described as animates, infants extended on the basis of both shape and texture. Experiment 3 revealed similar results for 1.5-year-olds. These results challenge the notion that expectations in word learning (e.g., the "shape bias") (a) emerge late and (b) rest entirely on correlations between perceptual object features and words. Instead, the results indicate that both perceptual and conceptual information permeate word learning in infancy.