Researchers have become increasingly interested in disentangling selection and influence processes. This literature review provides context for the special issue on network-behavior dynamics. It brings together important conceptual, methodological, and empirical contributions focusing on longitudinal social network modeling. First, an overview of mechanisms underlying selection and influence is given. After a description of the shortcomings of previous studies in this area, the stochastic actor-based model is sketched; this is used in this special issue to examine network-behavior dynamics. The preconditions for such analyses are discussed, as are common model specification issues. Next, recent empirical advances in research on adolescence are discussed, focusing on new insights into moderating effects, initiation of behaviors, time heterogeneity, mediation effects, and negative ties.Relationships with peers provide an important context for social development and adjustment. Two fundamental processes underlying network-behavior dynamics are key to our understanding of adolescents' development: selection and influence. Selection processes concern, for example, whom adolescents choose to hang out or be friends with. They affect the formation and dissolution of relationships. One important and well-known class of selection processes is based on similarity. Beginning in early childhood, children tend to sort themselves nonrandomly into friendships, selecting peers who are more or less similar to themselves. However, similarity is not the only possible basis of relationships. Selection processes refer more generally to any mechanism by which individuals adjust their relationships in response to the social context, their own behaviors, and their peers' behaviors.In contrast, peer relationships also shape individual behaviors and other changeable characteristics (e.g., attitudes and opinions). Whom adolescents hang out with and whom they consider to be friends affects their individual development. Influence processes refer more generally to individuals changing their behavior or attitudes in response to (the behavior or attitudes of) the peers they affiliate with.A methodological challenge here is that selection and influence processes might both result in the same empirical phenomenon: similarity of connected individuals. This similarity may result from similar individuals choosing each other (selection), which suggests that behavior remains similar, but relationships change, or from connected individuals becoming increasingly similar (influence), which suggests that relationships remain stable but behavior changes. This shows, first, that longitudinal analysis is necessary if one aims to assess selection and influence processes. Second, the sequence of changes in the network and the behavior represents the mutual dependence between network dynamics and behavior dynamics. It is, therefore, necessary to examine behavior and network dynamics simultaneously, using a method that is capable of accounting for this simultane...