The papers in this special issue apply two recent data analytic techniques to the study of family and close peer relationships. The Actor-Partner Interdependent Model incorporates the perspectives of both participants in a dyad into analyses that describe shared and unique views of the relationship. The Social Relations Model incorporates the perspectives of all members of a group into analyses that ascribe views unique to individuals and relationships, and views shared by the entire group. Developmental applications of techniques originally designed for concurrent interdependent data are described.