This publication constitutes the proceedings of the OECD conference on the “Environmental Uses of Micro-Organisms: An Overview of the State-of-the-Art and Implications for Biotechnology Risk/Safety Assessment”. This event, organised under the auspices of OECD’s Working Group on the Harmonisation of Regulatory Oversight in Biotechnology (WG-HROB), was held on 26-27 March 2012. A total of 100 participants attended the conference, which was open to OECD delegates as well as external scientists, regulators and interested individuals. It was developed in collaboration with the OECD Co-operative Research Programme under the Trade and Agriculture Directorate.