Environmental regulators approach odors not as a feature of the environment, but as something to be minimized and avoided. This regulation is based around the principle that it is possible to determine when odors will cause a nuisance. Evidence suggests that nuisance results from the strength of an odor, but also from its offensiveness, the duration of exposure and nature of the smelling population. Environmental scientists have investigated how odors result in annoyance. This chapter examines the evidence they use to determine when odors may be an issue for nearby residents, and discusses how we can design urban areas alongside industry.