Ten dyads were observed biweekly from 10 to 24 months of infant age while playing together at home with a set of toys. The aim was to examine whether mother–infant coregulation changes over the second year of the infant’s life and whether there are individual differences in that process. Normative trends as well as variability between and within dyads were tested using a multilevel modeling technique. We found that unilateral coregulation, in which only the mother was actively involved in play, largely prevailed at the beginning of the year and then decreased linearly, while symmetrical patterns, implying that the infant was also involved, were for the most part absent at the beginning but then increased rapidly, overtaking unilateral from the middle of the year on and becoming predominant by the end. In particular, symmetrical episodes of shared affect and shared action increased first and then decreased, being replaced by shared language. Variability in data was significant between the dyads, with some dyads advancing toward symmetrical coregulation at an earlier age and more rapidly than the others. It was also significant within the dyads, as the increase in symmetrical coregulation unfolded in a quite irregular manner across the sessions, unlike the decrease in unilateral. Results are discussed with reference to a view of joint attention development as a gradual and complex process.