Polluted air has become an increasing environmental and health concern. Legislation controlling the emissions of air Pollutants (VOC, toxics and odor) has proliferated. In recent years, biological techniques have been applied more frequently to control these emissions, because they eliminate many of the drawbacks of classical physical-chemical techniques. Different waste gases require different strategies for optimal and sustainable purification. Biological treatment provides an expanding variety of opportunities for economical and environmentally friendly solutions for many waste gas emissions. In Europe, a significant body of knowledge and experience has been generated on biological waste gas purification. Examples of some interesting developments and new applications of biological waste gas treatment systems in Europe during the last 5 years are presented in this paper. (c) 2005 Elsevier B.V. All rights reserved.