ABSTRACT Behavior patterns can be sustained across the life course by two kinds of person-environment interaction Cumulative continuity arises when an individual's interactional style channels him or her into environments that themselves reinforce that style, thereby sustaining the behavior pattern across the life course through the progressive accumulation of its own consequences Interactional continuity arises when an individual's style evokes reciprocal, sustaining responses from others in ongoing social interaction, thereby reinstating the behavior pattern across the individual's life course whenever the relevant interactive situation is replicated Using archival data from the Berkeley Guidance Study (Macfarlane, Allen, & Honzik, 1954), we present evidence for the operation of these two continuity-promoting processes by identifying individuals who were ill-tempered, shy, or dependent in late childhood and then tracing the continuities and consequences of these interactional styles across the subsequent