Successful navigation through the social world critically depends on how we perceive a face. Faces are the pre-eminent social signal from which we extract information related to the identity, age, sex, attractiveness, emotional state, and intentions of a person. All of these social cues help us anticipate the behavior of others and guide our decisions about how to behave towards them. Given the importance of face perception to our social functioning, one might expect to see mature abilities and neural specialization even in young infants. However, some aspects of face processing behavior and neural representation are not mature until adulthood. We argue that face-processing abilities are always changing developmentally based on social developmental tasks (SDTs) and the orientation of primary affiliative relationships. For example, the SDTs of childhood and adolescence are dramatically different. Children are focused on learning self-mastery and societal expectations, while still largely depending on primary caregivers. In contrast, adolescents are developing increasing autonomy from caregivers as they engage in confiding friendships and romantic partnerships with peers. Thus, the focus of the affiliative relationships fundamentally shifts from parents to peers during adolescence. We argue that this shift shapes the kinds of information that adolescents garner from faces, (e.g., the ability to perceive new kinds of expressions – like flirtatious – especially in peer faces). Furthermore, we argue that puberty causally influences this process by increasing the motivation to accomplish these new SDTs, which will require a re-organization within the neural network configuration of the existing face- processing system. To test this hypothesis, we will test pre-pubertal children, adolescents in early and later stages of pubertal development, and post-pubertal young adults in a battery of face-processing behavioral and fMRI tasks that are related to SDTs of early childhood (e.g., processing basic facial expressions), and those related to SDTs of adolescence (e.g., processing complex emotional expressions, attractiveness). In an unprecedented longitudinal design, we will test all adolescents every 3 months for up to 2 years to capture each individual’s own specific transition into the next pubertal stage. This will trigger a second testing session of the behavioral and fMRI tasks so that we can determine how a change in pubertal stage influences performance on these tasks and on the organization of brain networks for processing faces. This innovative longitudinal study will provide an understanding of the normative developmental trajectories involved in structuring and stabilizing neural networks underlying social information processing and understanding core mechanisms that influence this process. It will also have relevance for understanding how face perception is disrupted in so many disorders (e.g., social anxiety, depression, schizophrenia, bipolar disorder, autism) that effect social interactions and relationships with other people.