This study examined the development of shyness in 37 children (20 boys and 17 girls) followed longitudinally from the first months of life, analyzing maternal responsiveness at 16 months as a possible mediator in the relationship between fear of novelty at 4 months and shyness at 16 months. Data were collected at two different time points. At time 1 (age 4 months), mothers were asked to provide some sociodemographic information and to complete an infant temperament questionnaire. At time 2 (age 16 months), families were visited at home in order to observe the child's behavior in front of an unfamiliar adult and maternal responsiveness in a naturalistic setting. In addition, toddlers' shyness was assessed through a temperament questionnaire. Results show that 1) there is a relation between fear of novelty at 4 months and shyness at 16 months; 2) there is a concurrent relation between toddlers' shy behavior and maternal responsive behavior at 16 months; 3) the relation between fear of novelty at 4 months and shyness at 16 months is mediated by maternal responsiveness assessed at 16 months when the child is confronted with an unfamiliar adult.