The preferences of 2- and 4-month-old infants for consonant versus dissonant two-tone intervals was tested by using a looking-time preference procedure. Infants of both ages preferred to listen to consonant over dissonant intervals and found it difficult to recover interest after a sequence of dissonant trials. Thus, sensitivity to consonance and dissonance is found before knowledge of scale structure and may be based on the innate structure of the inner ear and the firing characteristics of the auditory nerve. It is likely that consonance perception provides a bootstrap into the task of learning the pitch structure of the musical system to which the infant is exposed.