### Key points Ventilator-associated pneumonia (VAP) is the most common healthcare-associated infection (HAI) in adult critical care units.1 It is associated with increased intensive care unit (ICU) stay, patient ventilator days, and mortality.2 VAP is thought to increase the mortality of the underlying disease by ∼30%.3 At present, there is no consensus definition for VAP, although many have been proposed. VAP is complicated by the lack of a consensus ‘gold standard’ definition to test the accuracy of potential diagnostic criteria. This article reviews the currently used diagnostic criteria, the role of care bundles and other novel techniques in VAP prevention, and recent advances in surveillance systems to overcome the diagnostic difficulties. Currently, the diagnosis of VAP is based on a combination of clinical, radiological, and microbiological criteria. There are a wide range of clinical conditions that mimic VAP in ventilated patients, including acute respiratory distress syndrome (ARDS), pulmonary oedema, pulmonary contusion, tracheobronchitis, and thromboembolic disease. Some of the clinical features used to define a VAP (e.g. change in tracheal secretions) are subjective and are subject to inter- and intra-observer variation. The diagnostic value of these clinical criteria in isolation, and in combination, has been reviewed recently by Klompas.4 While individual clinical criteria appear to lack clinical sensitivity, combination of clinical criteria with laboratory criteria and radiological features improves the accuracy of a clinical diagnosis. …