I have tested the hypothesis that infants are born with a capacity for social interacting and, that from an early age they can engage in an intersubjective relationship, not only with their mothers, but with other infants. I also investigated the sensitiveness of paired infants to the motives and feelings of their partners. I measured turn-taking, imitation, and both local and general bodily emotional expressions of their partners. I measured turn-taking, imitation, and both local and general bodily emotional expressions of a reciprocal or complementary form. Results show that 6 month-olds try to make contact, but, they do not sustain interaction. As a result, invitations for interactions occur frequently, but they are not always followed by appropriate responses. The infants are very interested and very friendly to one another, but as a result of their inability to keep attention, they often show indifference. At 8 months, infants show less indifference. They keep their interactions going for longer periods, and show much more interest in the other infant, with no irritation. At 9 months, another change is evident. Interactions and invitations are more balanced, meaning that the older infants are trying to give the partner turns in interactive strategies. At all ages, girls were more interactive, showing more emotional expressions than boys. Imitation is present in all ages, and at a very significant rate. It seems that infants use imitations to assist and regulate interaction: to start it, to keep it with more positive emotional expressions. This result is opposite to the differences between boys and girls observed in the Cross-Sectional and Longitudinal studies, where girls were more responsive. At all ages, infants are very attentive to their mirror images, which attract them and excite a richer variety of expressions than they display when faced with another infant. An important finding is that the 6-month-olds showed clear evidence of self-recognition in their emotional expressions and interactions.