Recent contributions to firm environmental policy claim that the link between environmental management systems (EMS) and firm performance still remains unanswered. From a natural‐resource‐based view (NRBV), the effective implementation of EMS inside the firm requires complementary organizational capabilities and resources to deploy proactive environmental strategies. In this research, we develop an empirical model using an improved measurement of EMS, which considers not only ISO 14001/EMAS certification but also its maturity (time elapsed since certification or verification), and propose an indirect effect on firm financial performance through the mediating role of green corporate image. Empirical results tested in a sample of Spanish manufacturing firms offer new insights into the NRBV and EMS literature debates. Copyright © 2015 John Wiley & Sons, Ltd and ERP Environment