A growing number of governments seek to adopt an approach based on Best Available Techniques (BAT) as part of the regulatory framework to prevent and control industrial emissions. Providing guidance on BAT-based permitting is, in the short term, a means to strengthen policy in individual countries. In the long term, it might facilitate greater international harmonisation of procedures to establish BAT and BAT-AE(P)Ls. This would assist efforts to protect human health and the environment across countries, and expand the level playing field for industry. This document presents a high-level overview of each step of the process to determine BAT, BAT-AE(P)Ls and permit conditions, including information on the principles and factors that should be considered in this process, based on best practices from OECD member and partner countries. It provides references to more detailed information from countries where such approaches are employed, and includes a range of elaborate examples from national and supra-national jurisdictions as well as international conventions. The document promotes an integrated approach to BAT-based environmental permitting. This is the fourth in a series of documents developed as part of the OECD’s BAT project.