Since 1995, Canada’s Commissioner of the Environment and Sustainable Development (the Commissioner) has been providing parliamentarians with objective, independent analysis and recommendations on the federal government’s efforts to protect the environment and foster sustainable development. This chapter presents an overview of the work of the Commissioner, including the institutional setting within the Office of the Auditor General of Canada. The first section provides the historical background about the office. The second section describes the Commissioner’s role and functions, and the third section comments on the audit function as a model for other countries, focusing on attributes of effectiveness. The final section offers concluding comments.