Whether to treat localised respiratory disease, or because the lung provides a fast, non-invasive, and efficient route of delivery for systemic effect, the administration of pharmaceuticals to the lung is gaining increased attention; even beyond treatments for globally prevalent diseases like asthma and chronic obstructive pulmonary disease (COPD). Although well established and accepted, oral and parenteral administration of drugs may require much higher doses than topical administration to the lung and can lead to significant unwanted systemic exposure and side effects. However, the lung also presents unique challenges because of the complex structure of the airways, the presence of various protective barriers, and the need to form a suitable aerosol using an inhaler.