Selective collapse of a lung and one-lung ventilation (OLV) is now performed for most thoracic surgical procedures. Modern double-lumen endobronchial tubes and bronchial blockers have made lung separation safe and relatively easy to achieve. However, OLV in the patient with a 'difficult airway' can present a challenge to the anaesthesiologist. This review considers the different techniques used to achieve lung separation and their application to the patient with a difficult airway.