To evaluate the extent to which infants and mothers are able to coordinate their behavior, the interactions of 54 mother-infant pairs--18 each at 3, 6, and 9 months of age--were videotaped. Coordination was evaluated with 2 measures: (1) matching--the extent to which mother and infant engage in the same behavior at the same time; and (2) synchrony--the extent to which mother and infant change their behavior with respect to one another. Mother-infant pairs increase their degree of coordination with infant age, but the proportion of time they are coordinated is small. Mother-son pairs spend more time in coordinated states than mother-daughter pairs. The results suggest that interactions be characterized in terms of their movement from coordinated to miscoordinated states rather than only in terms of their degree of coordination. The gender differences are discussed in terms of their importance for the developmental differences in females and males.