Since establishment of the ISO 14001 environmental management system in 1996, Japanese facilities have led the world in numbers of certifications. This research utilises survey data from more than 1700 Japanese facilities as well as follow-up interviews to identify the determinants of ISO certification, to examine the differences between early, recent and in-process certifiers, and to understand how ISO 14001 certification affects various environmental and managerial outcomes in Japan. Findings show that ISO certified facilities are larger and report higher levels of environmental management capacity. In addition, early certifiers are more likely to have established voluntary environmental agreements and are more active in international trade and business. Findings also provide evidence that while many facilities believe that ISO 14001 certification is excessively costly, they also report that certification has resulted in the establishment of new energy efficiency and waste reduction targets and higher target levels. Nevertheless, evidence indicates that certification does not generally result in longer-term outcomes such as post-certification adjustment of non-regulated targets.