Numerous dimensions of the peer social networks of children with Down syndrome were examined within a developmental framework. Results revealed that for many key measures, particularly involvement in play, linkages to other settings, and control of play, children with Down syndrome have less well-developed peer networks even in comparison to a mental age matched group of typically developing children. This suggests both an absence of any social advantage in the peer context for children with Down syndrome and the existence of unusual difficulties that may be traced to underlying problems in peer-related social competence. The need for future observational studies of peer interactions for this group of children was emphasized.The social networks of young typically developing children gradually expand to include increasing numbers of peers throughout the preschool years. The contexts for these relationships vary considerably and include informal contacts with individual children in home or community settings as well as contacts that occur in more structured activities, such as organized playgroups, preschools, or child care. Parents eagerly support the formation of these peer social networks (Ladd & Pettit, 2002) and attach considerable importance to their young child's emerging relationships with their peers (Mize, Pettit, & Brown, 1995). It is usually within these peer social networks that young children form preferences for and establish regular contact with one or more children, thereby forming early friendships characterized by varying degrees of reciprocity, mutuality, and shared affect (Rubin, Coplan, Chen, Buskirk, & Wojslawowicz, 2005). The emergence of these peer networks constitutes an important index of children's social integration within their communities and provides opportunities for children to further develop their social skills (Newcomb & Bagwell, 1995, 1996.Mothers of young children with developmental (cognitive) delays also attach considerable importance to and actively help establish their children's peer social networks (Booth, 1999;Guralnick, Connor, & Hammond, 1995). Nevertheless, even when considering contacts with peers that occur in home settings, the peer social networks of young children with developmental delays are more limited than those of similar age typically developing children (Guralnick, 1997;Lewis, Feiring, & Brooks-Gunn, 1988;Stoneman, Brody, Davis, & Crapps, 1988). Although many factors are at work, including negative attitudes towards individuals with disabilities, these peer social network limitations appear to be related to the unusual and pervasive peer social competence difficulties exhibited by this group of children (see Guralnick, Hammond, Connor, & Neville, 2006). In fact, evidence suggests that children with delays exhibit difficulties in peer competence even beyond those that would be expected based on their cognitive levels (Guralnick, 1999a(Guralnick, , 1999b.Correspondence regarding this article should be sent to Michael J. Guralnick, Center on Human ...