While there is little empirical evidence to demonstrate which types of environmental management systems (EMSs) are associated with greater environmental improvements, governments worldwide are encouraging facilities to adopt them. This research compares the environmental performance of facilities that adopt ISO 14001–certified EMSs, complete (noncertified) EMSs, and incomplete EMSs across multiple environmental media. The authors analyze these relationships for manufacturing facilities in seven countries using a two-stage model to control for selection bias. Findings indicate that the adoption of all types of EMSs is related to improved environmental performance in an international setting. However, ISO 14001–certified EMSs are associated with environmental improvements to a broader array of environmental media. These findings offer important implications about which types of EMSs have greater promise as voluntary environmental governance tools.