Babies, who look like helpless blobs, are capable of impressive feats of learning. 3-year-olds, who can't cross the street alone, know an astounding amount of information about their environments. We will focus on landmark studies that elucidate how children's biology, cognition, language, and social experiences interact to set the stage for what we do and who we are. Is the baby's world a 'blooming, buzzing confusion', or do babies enter the world prepared to make sense of their environments? How can we understand the collaboration between nature and nurture during development?