The lung reacts in a limited number of ways to insults—cough is its commonest response. The designation of a period for distinguishing acute from chronic  cough is somewhat arbitrary. Nevertheless, a cough lasting more than 3 weeks may be considered chronic. A specific aetiology for chronic cough is implicated in the vast majority of cases (McGarvey and Chung, Clinical assessment of cough. In: Chung KF, Widdicombe JG, Boushey HA (eds) Cough: causes, mechanisms and therapy. Blackwell Publishing, 2003). In spite of all investigations, the cause of a chronic cough may elude identification in 10–25% of patients—thus constituting the unfortunate wastebasket term of “chronic idiopathic cough” (Silvestri and Weinberger, Evaluation of subacute and chronic cough in adults, 2017). A cough labelled as “idiopathic” and attributed to a decrease in threshold of the sensitivity of the cough reflex (Haque et al., 2005) may later prove to have a specific cause In this chapter, a systematic approach to this ubiquitous symptom of respiratory disease is outlined.