The primary goal of this research is to increase the goodness-of-fit between the theoretical tenets of family systems theory and quantitative methods used to test systems hypotheses. A family systems perspective is applied to two specific research questions concerning family influences on adolescent development: To what extent are familial risk and protective factors for psychopathology and competence shared or not shared by siblings and are different family relationship patterns associated with optimal adolescent adjustment in nondivorced and remarried families? Multirater and multimethod data from a national sample of 516 nondivorced and remarried families from the Nonshared Environment and Adolescent Development (NEAD) project were examined using a combination of cluster, factor, and regression analyses. Results indicated that the effects of an individual relationship on adolescent adjustment is moderated by the larger network of relationships in which it is embedded. Evidence for nonshared familial processes in predicting adolescent psychopathology was also found but only in a subset of families, and the mechanisms of influence were neither main effects nor linear, as has been assumed by research to date. Results are discussed in light of family systems models of relationship influences on development. These results illustrate how family systems theory provides a specific example of contextualism as regards the development of psychopathology in adolescence.