The purpose of this study is to provide an in-depth understanding of safety behavior by testing a comprehensive model of safety organizational citizenship behavior (OCB). Informed by social learning theory (SLT), we argue that leaders play an active role in fostering safety OCB and examine two pathways through which servant leadership (SL) relates to this form of discretionary work behavior. Using structural equation modeling (χ2 = 229.81; df = 144; p< .05; TLI = .93; CFI = .95; RMR = .03; RMSEA = .06), we found that SL is positively related to safety climate (β = .28, p< .01)and collective efficacy (β = .22, p< .05), controlling for transformational leadership (TFL). We also found that safety climate (β = .34, p< .01) and collective efficacy (β = .46, p< .01) are both positively related to work unit safety OCB. Overall, our results suggest that safety climate and collective efficacy fully mediate the SL-safety OCB relationship. Using moderated hierarchical regression, we found that TFL moderated the positive influence of SL on safety climate (β = .23, p< .01) and collective efficacy (β = .18, p< .05), respectively, such that the influence was stronger when TFL is high than low. The interaction accounted for 5% and 3% increase in explained variance in safety climate and collective efficacy, respectively. Finally, we found that safety climate moderated the collective efficacy-safety OCB relationship (β = .25, p< .01) such that the influence was stronger when safety climate was high than low, accounting for 4% increase in explained variance in safety OCB.