Margaret Mahler's thinking, revolutionary for its time, led to the observational study of mother-infant pairs, followed almost day by day as the preverbal infant developed into a toddler whose increasing cognitive capacities made new demands on the mother's presence and emotional availability. The rapprochement crisis, as formulated based on these observations, is reexamined in the light of contemporary theory, and the concept of co-construction is used to show how mother and toddler repair misunderstandings and inevitable conflicts. With the growth of new verbal capacities during rapprochement, the toddler moves from early, sensorimotor interactions to interactions governed by language, in the process gaining new understanding of his or her emotional life.