Holger Daims is Associate Professor at the Department of Microbiology and Ecosystem Science at the University of Vienna, Austria. He received his PhD in Microbiology at the Technical University in Munich, Germany where he studied the ecology of nitrifying bacteria (especially nitrite-oxidizing bacteria) in biological wastewater treatment plants and developed tools to detect these mainly uncultured organisms in situ. In 2003, he became a founding member of the Department of Microbial Ecology at the University of Vienna in Austria. As University Assistant he established his own research group based on third-party grants. Subsequently, he was Assistant Professor from 2010 to 2012, obtained his “Habilitation” (venia docendi) for Microbiology in 2012, and became Associate Professor in 2012. His research addresses the ecology, physiology, and evolution of nitrogen-cycling microorganisms with focus on nitrite-oxidizing bacteria, and the development of molecular and imaging methods to study uncultured microorganisms in natural and engineered ecosystems.