Infants are social beings who are born with innate reciprocal communication skills that can be observed during the two first months after delivery in babies with normal development. These skills include abilities to make and maintain eye contact, to vocalize and to use facial expressions, body and head movements to start interactions. Micro-analytical studies have demonstrated the frequent appearance of short episodes of social withdrawal affecting the infant during mother-baby interactions, whose function is to regulate the interaction flow. This behavior can be perceived when the infant needs to calm down or when is tired, and as a reaction to transitory interaction disturbances. In contrast with these short episodes of social withdrawal, the occurrence of sustained social withdrawal in infants is significantly less and is frequently associated with pathological conditions, such as autism spectrum disorder, child depression, and severe or chronic pain. Additionally, sustained social withdrawal is a symptom of anxiety and post-traumatic stress disorders. Different studies have revealed a prevalence of 10-14% sustained social withdrawal in term infant populations and of 13-22% in pre-term infant populations. In addition, the increase in sustained social withdrawal has been related to deviations of the interaction skills, attachment, as well as to relational and behavioral disorders. The increase and chronification of sustained social withdrawal, used as a defensive conduct, imply a risk to the adequate development of an infant's potential and raise the probability of alterations in the development of his psychopathology.