To their everyday life with children, parents bring a number of ideas about development and about parenting. Some of these ideas are about their own children and about themselves as parents. Others are more general: ideas, for instance, about what babies are like, how children change with age, what kinds of affection and control they need, the responsibilities of mothers and fathers, or the degree of influence each parent has over the way a child develops. Moreover, the ideas that parents hold, shape their actions with children and the way they assess both their children and their own performance as parents. With the recognition of parental thinking as a powerful factor in family life, research has turned to the study of this `everyday' or `informal' psychology. Some of the studies deal with the nature of parents' ideas: What ideas are held? Which are most widely shared? How do these ideas differ from one another? Some deal with the sources of parents' ideas: with the factors that give rise to differences among parents from different backgrounds (different cultures, different economic groups, different degrees of experience with children). Others concentrate on the consequences of parents' ideas for themselves and for children. This monograph summarizes the research with an eye to several audiences (researchers, clinicians, educators) and with an emphasis on the questions that remain. A major goal is to point not only to significant gaps, but also to some specific ways in which they might be addressed by further research.