The 3rd Annual Conference on Metagenomics and Metadesign of the Subways and Urban Biomes (MetaSUB), hosted in conjunction with The Wenner-Gren Institute, Stockholm University, was held on July 18-20, 2017, in Stockholm, Sweden at the Royal Swedish Academy of Engineering Sciences (www.iva.se). Our gracious host for this year was Dr. Klas Udekwu