Studies of infant speech perception have focused primarily on the ability of young infants (a) to make simple auditory discriminations, (b) to categorically discriminate speech sounds and (c) to exhibit perceptual constancy for phonetic categories. The first decade of developmental literature for stop consonants, vowels, and other speech and nonspeech contrasts is examined from these three perspectives. In addition, research into the origins (ontogenetic and phylogenetic) of these abilities is discussed, along with the studies that have probed the psychological and physiological processes that underlie the infant''s speech perception accomplishments.