KEYWORDS infant pulmonary function; pulmonary function; infant; thoracic compression technique; infant physiology A number of technologies have been developed to assess airway physiology in health and disease in infancy. The most commonly used in research related publications include assessment of resistance and compliance of the respiratory system, analyses of tidal volume parameters, various methods of measurements of flow, assessment of lung volume by gas washout or plethysmography, and measurements of gas mixing to assess ventilation inhomogeneity. Physiologic measurements of the infant airway have been most frequently used in longitudinal studies of populations. Such applications have elucidated aspects of airway and lung development, and have given insights into airway size as a contributing factor to wheezing, airway hyperreactivity, as well as the natural history of diseases such as RSV infection, bronchopulmonary dysplasia, and cystic fibrosis. A frequently quoted example of an important application of infant pulmonary function tests (IPFT) is the series of studies conducted in Tucson, Arizona, over the last 2 decades, which were seminal in furthering the understanding of the development of wheezing in infancy and early childhood. 1 The utility of these techniques for assessment of health and disease in individuals, has been more limited. A comprehensive review of the whole range of IPFT is unrealistic within the scope of this session on the wheezy infant, and I will therefore focus on