Research concerning a supplier’s voluntary adoption of environmental practices has focused on buyer influence and supplier leadership values. These explanations are pertinent to early adopters, but other theoretical perspectives are needed to understand why later adopters, who tend to be more conservative, may or may not be likely to adopt environmental practices. Two theoretical lenses may be used to better understand later adoption processes. First, transaction cost economics examines implementation costs that have not been considered in previous research. A transaction cost economics perspective suggests that suppliers are more likely to adopt environmental practices if their information seeking, bargaining, and enforcement costs are minimized. Second, institutional theory can be applied to drivers within the supply base. The institutional theory analysis reveals that supplier adoption of environmental practices is more likely if coercive, normative, and mimetic institutional forces are in play.