Biological scrubbing is an important technique employed in the reduction of gaseous or vaporous emissions. It can be applied both as the only purification stage and in connection with other techniques. The guideline VDI 3478 Part 1 deals with the conditioning and biological scrubbing of waste gas flows which are contaminated by gaseous and/or particulate solid and liquid air-polluting substances. In the many applications, the focus is placed on the reduction of organic and odour-intensive gases and vapours which are water-soluble and biodegradable at sufficient speed. The guideline gives an overview over the process-related principles, the design and construction of plants, the process variants and their operation as well as typical application examples.