Just as each person develops from infancy to adulthood, all interpersonal relationships have a life history that encompasses the changes in how people communicate with each other. This book is about how a relationship transforms itself from one pattern of communication to another. The authors present a unique research method called 'relational-historical research', based on advances in dynamic systems theory in developmental psychology, and qualitative methods in life history research. It rests on three premises: that the developing relationship (not the individual) is the unit of analysis; that change emerges from, but is not entirely constrained by, the patterns of the past; and that the developmental process is best revealed by making frequent observations within a particular case before, during, and after a key developmental transition. Looking specifically at the mother–infant relationship, this is a compelling piece of research that will appeal to an international audience of intellectuals and practitioners.