CPAP is basically a device based on the creation of expiratory resistance. A conceptual model attempts to simplify the basics of expiratory resistance. The earlier devices used continuous gas flow and the expiratory resistance was created by an underwater chamber. The height of the tubing inside the water determined the level of CPAP (bubble CPAP). CPAP in continuous flow device is based on the creation of expiratory resistance from the exhalation valve. The expiratory valve if closed partially during expiration will lead to inadequate air emptying and the creation of positive pressure at end expiration (PEEP/CPAP). The degree of occlusion of expiratory valve determines the degree of PEEP/CPAP. Variable flow sophisticated machines incorporated specialized physical principles to reduce the resistance during expiration and in the process the work of breathing. Various devices used to generate and deliver CPAP, their principle, advantages and disadvantages are described. Variable flow nasal CPAP recruits lung volume more effectively than the 2 continuous flow devices at similar CPAP levels. Comparison of various CPAP delivery interface including nasal prongs, nasal mask, and nasopharyngeal tube is described. In INSURE the baby is administered surfactant early and then extubated to CPAP thereby preventing the damage that ensues from mechanical ventilation. Technique and steps in INSURE procedure is described.