Coughing is a normal function that serves to expel secretions from the airways, prevent inhalation of material into the airways and delay entry of material deeper into the lungs. It is therefore an extremely important mechanism in the protection of the respiratory system. This raises the issue of control of coughing in disease situations, where the benefits of coughing might outweigh the benefits of supressing the cough. In fact, in some situations, such as chronic bronchitis, stimulating coughing by chest coupage is believed to be therapeutically beneficial. The following are addressed: Mechanism; Causes; Differentiation between cardiac and respiratory origin; and Differential diagnoses for respiratory causes.