The literature on certifiable management standards has not paid sufficient attention to implementation of standard requirements in certified firms. Firms that obtain standard certification to achieve the legitimacy benefits of certification may not implement standard requirements sufficiently to realize the standard’s intended performance outcomes. We argue that such decoupling of implementation from certification threatens the effectiveness of certifiable standards as governance mechanisms for firms’ environmental conduct because standard certification may not accurately signal firms’ superior environmental performance to external stakeholders. Empirical findings based on the ISO 14001 standard at the facility level support this view: Quality of standard implementation affects facilities’ environmental performance, and environmental performance of certified and non-certified facilities does not differ significantly for the overall sample and low-quality implementers, while high-quality implementers have better environmental performance than their non-certified counterparts. We provide recommendations for increasing the effectiveness of governance systems for firm conduct based on certifiable standards.