The delivery of drugs to horses via the inhalation route is being increasingly adopted as a therapeutic approach in equine practice; predominantly used to treat equine lower airway disease, including, but not restricted to, severe and mild to moderate equine asthma (previously termed recurrent airway obstruction and inflammatory airway disease, respectively), and exercise-induced pulmonary haemorrhage. Like many therapeutic approaches, there are both advantages and disadvantages associated with inhalation therapy that must be considered when selecting the most appropriate treatment. Additionally, there are a number of unanswered questions with respect to inhalation therapy in the horse, most notably in relation to the efficiency and variability of drug delivery to the lower airways, which most commonly constitutes the principal target site of drug deposition. Even in the absence of lower airway disease, achieving such drug deposition within a system designed to avoid particle penetration of the lungs can be challenging. This review discusses the principles of inhalation therapy, the advantages and disadvantages of this approach, the techniques commonly used to administer inhaled medication and the drugs commonly administered via the inhaled route.