Role breadth self-efficacy (RBSE) refers to employees' perceived capability of carrying out a broader and more proactive set of work tasks that extend beyond prescribed technical requirements. A newly developed scale of RBSE was internally consistent and distinct from the related concepts of proactive personality and self-esteem. In an initial cross-sectional study (N = 580), work design variables (job enrichment, job enlargement, and membership of improvement groups) were the key organizational predictors of RBSE. These investigations were repeated in a second cross-sectional study (N = 622) and extended by examining change over time (N = 459). The longitudinal analysis showed that increased job enrichment and increased quality of communication predicted the development of greater self-efficacy.