The ethological approach is suggested as a fruitful research strategy in the study of how infants express emotions. This approach led to the development of a large catalogue of facial/vocal behaviors that was used in the systematic observation of 75 girls and boy infants in the later quarter of the first year of life placed in a series of standardized laboratory situations. Each of the 42 facial expressions contained in the catalogue are precisely defined according to the expressive elements of the brow, eyes, mouth, and other facial regions. The vocalizations are also operationally defined. The possible ways that the facial expressions and vocalizations could be combined in the expression of emotional behavior in infants are discussed. (36pp.)