Although understanding the relationship between the individual and work environment is a core concern of organizational research, few studies have examined longitudinal transactions between Big-5 personality traits and job characteristics. Building on research in personality and job design we develop hypotheses detailing transactions between Big-5 personality traits (i.e., openness, conscientiousness, extraversion, agreeableness, neuroticism) and two key job characteristics (i.e., job discretion and workload). Specifically, we hypothesize and test transactions with regard to the effects of job characteristics on personality, the effects of personality on job characteristics, and the reciprocal effects between these constructs. Our findings, based on a latent change score analysis of data collected over three waves across 20 years, show strongest support for the effects of job characteristics on personality, particularly the effects of workload on personality change in openness, extraversion, and agreeableness. We found no effects of job discretion on personality, limited support for the effects of personality on job characteristics (except a positive effect of neuroticism on job discretion), and no evidence of reciprocal effects. Practitioner points: Job demands can alter employee personality. Employees who consistently experienced high workloads over a 20-year period incurred developmental increases in three personality traits – extraversion, openness, and agreeableness – such that they became more outgoing and assertive, more curious, and broadminded, as well as more helpful and sympathetic. Employees who experienced high job discretion did not incur similar development changes in personality.