The present study was aimed at examining one relatively neglected part of the identity formation process: the short-term dynamics of identity formation. The short-term dynamics were assessed by examining (a) the day-to-day course of 2 key dimensions of identity formation (i.e., commitment and reconsideration) and (b) the impact of fluctuations in commitment and reconsideration on subsequent levels of these 2 dimensions. Longitudinal data on 580 early adolescents (54.8% boys, 45.2% girls) were used to test these assertions. The authors found evidence for a commitment-reconsideration dynamic that operated on a day-to-day basis. Furthermore, the findings confirmed E. H. Erikson's (1950) assertion that identity reflects a sense of sameness and continuity as a more stable identity (reflected by little day-to-day fluctuations) was predictive of higher levels of commitment and lower levels of reconsideration. Taken together, the present study underscores the importance of the short-term dynamics of identity formation. © 2010 American Psychological Association.