This 4-wave longitudinal study of newcomers in 7 organizations examined preentry knowledge, proactive personality, and socialization influences as antecedents of both proximal (task mastery, role clarity, work group integration, and political knowledge) and distal (organizational commitment, work withdrawal, and turnover) indicators of newcomer adjustment. Results suggest that preentry knowledge, proactive personality, and socialization influences from the organization, supervisors, and coworkers are independently related to proximal adjustment outcomes, consistent with a theoretical framework highlighting distinct dimensions of organizational and work task adjustment. The proximal adjustment outcomes partially mediated most of the relationships between the antecedents of adjustment and organizational commitment, work withdrawal, and turnover.