Historically, the evolution of inhalation therapy can be traced to India 4000 years ago. The antecedents of contemporary inhalation therapy, however, began in the nineteenth-century industrial age with the invention of the glass bulb nebulizer. From there, inhaler technology evolved along two pathways characterized by refinements in existent nebulizer technology and the invention of a portable inhalation device, the metered-dose inhaler (MDI). More recently, growing recognition of problems associated with MDI use (chiefly, its reliance on coordinated patient inhalation and actuation technique) led to modifications in the MDI itself with auxiliary devices (spacers) and the development of new inhaler systems--dry powdered inhalers (DPIs) and the breath-actuated metered-dose inhaler (BAI-MDI).