Three kinds of achievement evident in the contributions to this issue are discussed. First, the systematic evidence for significant bidirectional effects in parent-child relationships is considered and some key principles are highlighted. Second, the information on the nature of parent-child relationships, as in the studies of discipline and play, is considered. Third, challenges and questions raised by, but not necessarily answered in, the articles are considered, with a focus on four topics: the processes implicated in bidirectional influence, the issue of how different levels of analysis illuminate but also constrain the kinds of conclusion that can be drawn, the issue of how developmental change affects patterns of influence within parent-child relationships, and the issue of our biases in interpreting patterns of influence within parent-child relationships.