Air leaks are one of the most common complications after pulmonary resection and they are the most frequent cause of prolonged hospital stay, increased cost and patient dissatisfaction. The management of chest tubes in patients with air leaks is optimized when the air leak is scientifically evaluated. The traditionally used analogue classification system, the Robert David Cerfolio Classification System (or RDC named after my father) has inherent subjectivity to it and may be interpreted differently by different bedside observers. More recently, several companies have developed digital pleural drainage systems that are able to quantify the size of air leaks in ml/min or in ml/breath. This eliminates the subjectivity. This affords better interpretation of chest tube setting changes and of air leak healing. These units also provide recordings of the air leak and of the pleural pressure. In this multimedia chapter, we report the different methods of measuring air leaks.