New Zealand's forest industry has several codes of practice available for erosion and sediment control. This article reviews conditions required for a code of practice to succeed in protecting the environment. Internal conditions – those conditions which are written into a code and can be assessed by reading the document alone – were used to assess the strengths and weaknesses of six of New Zealand's forest codes of practice. The study found that overall, the codes scored highly for objectives, communication, planning and comprehensiveness. However they did not score well for regulatory approach, monitoring, foundations and review process. Some preliminary recommendations were made about the development of future codes of practice based on these results.