Commentary: siblings in their families.

Three themes in the contributions to the Special Issue are discussed. The first is new evidence for associations between the quality of sibling relationships and children's adjustment problems and positive development, from research which also takes account of parent-child relationships, and genetic associations. The second is the new methodological approaches to studying the complexity of family patterns in which siblings play a central role (for instance with multilevel modelling) and the study of changes over time. The third is the significance of connections with relationships outside the family especially peer relationships and friendships.