Equine asthma is an umbrella term defined by nonseptic lower airway inflammation. Currently there are two broad categories, namely mild to moderate equine asthma (formerly known as inflammatory airway disease) and severe equine asthma (formerly known as recurrent airway obstruction or heaves). Environmental challenge is involved in the aetiopathogenesis of both these subcategories. Much of this challenge, and the part that we can control, is provided by the organic dust associated with the stabling of horses. This article reviews the available evidence relating to the environmental management of equine asthma and tries to relate this to practical options for providing a low-dust environment.