Continual improvement is a key component of ISO 14001, but in contrast to most other specifications in the standard, it is difficult to assess. Based on interviews with 19 certified companies in the chemical, food, and environmental services sectors, this article explores the dynamics of continual improvement. While most auditing practices focus on the operational level of improvement, the system level is more important in realizing continual improvement. Taking continual improvement as an explicit principle, defining long-term objectives, and widening the scope of environmental policy objectives can be used as indicators for system level improvement. Front-runners in continual improvement tend to use more management indicators and think more favourably on benchmarking. They are relatively stronger motivated by internal policy ambitions, and parent company aims than by pressures from outside. Further elaboration of performance frameworks for continual improvement is needed, taking into account the way performance indicators can stimulate internal motivational, and policy processes.