Although a sense of mastery is usually treated as a stable personal resource that can moderate the effects of stress on well-being, in this article we are interested in mastery as an outcome, examining the impact of transitions in the careers of Alzheimer's caregivers on their sense of mastery. Using longitudinal data collected from 456 spouses and adult children caring for a family member with Alzheimer's disease, we found that for those who continue to care for their relative, mastery declines; for those who place their relative in a care facility, mastery remains unchanged; and for those who experience the death of their relative, mastery increases. A series of regression analyses revealed different patterns of predictors of change in mastery over time and across transitions.