Urban indoor air quality (IAQ) is an international health issue, since city dwellers spend 90% of theirtime indoors. Research by a number of authors is reviewed here, demonstrating a range of capacitiesof indoor plants to improve IAQ and promote occupant wellbeing. Our laboratory studies, with nineindoor plant species, and our field studies in 60 offices, show that potted-plants can reliably reducetotal volatile organic compound (TVOC) loads, a major class of indoor pollutants, by 75%, to below100 ppb. They work equally well with or without air-conditioning, and in light or dark. An evaluation ofthese studies is presented, plus novel research showing that potted-plants can also remove indoor COand, sometimes, CO2. The evidence overall clearly shows that the potted-plant microcosm representsan innovative technology for solving indoor air pollution, which can otherwise cause a range ofadverse health effects, including building-related illness. This portable, flexible, attractive, low-costtechnology can complement any engineering measures and can be used in any building. To ensuresustainability of the urban environment, satisfying the triple bottom line of environmental, social andeconomic considerations, indoor plants can be expected to become standard technology for improvingIAQ - a vital building installation element.