This study extends existing research about how peers and leaders influence newcomers' adjustment to an organization or profession by examining how specific trust perceptions evolve over time. We test a model of how affect-based trust in one's leader and work unit peers develops from a basis of cognition-based trust and later influences organizational identification and role-related performance. U.S. Army soldiers were examined at the beginning, middle, and end of an intensive 14-week residential entry program of training and collective socialization. Cross-lagged structural equation analyses supported a causal relationship of individuals' cognition-based trust on affect-based trust directed toward their unit peers and, separately, their leaders. Individuals with high levels of chronic relational identity exhibited a stronger time-lagged relationship between cognition-based trust and affect-based trust for trust in peers, but not for trust in the leader. Affect-based trust in the leader had lagged influences on organizational identification and role-related performance at Time 3. Affect-based trust in peers was related over time to organizational identification but not role-related performance. We discuss the implications of these findings for understanding the separate influences of social exchange and social identity processes on newcomer adjustment, with distinct roles played by peers and leaders.