Increasing numbers of children experience parental separation and formation of stepfamilies. Research into the impact of these family transitions on children's adjustment by family sociologists and psychologists has greatly increased; changes in research perspectives over the last two decades are discussed, including a focus on individual differences in children's responses and the risk and protective factors implicated, on parent-child relationships as mediators of adjustment, on the significance of within-family differences and of biological relatedness (not solely family type), and on intergenerational patterns of associations. The importance of taking account of children's perspectives on family change, and of including investigation of children's relationships and experiences beyond the immediate household, to clarify the significance of children's relations with their nonresident parents and grandparents is increasingly recognized. Controversial issues are noted, and the lessons learned for research design, if we are to understand better the implications of these family changes, which are of major social and developmental significance, are summarized.