Bronchiectasis is a chronic lung disease that is characterised by excessive sputum production due to chronic airway inflammation. Physiotherapists use airway clearance techniques (ACTs) to assist with sputum clearance in people with bronchiectasis. Some of these techniques may involve positive expiratory pressure (PEP) devices. PEP devices provide a resistance to expiration which creates a back pressure in the airways which has been shown to enhance sputum clearance through stabilising the airways during expiration and improving alveoli filling via collateral channels. A simple PEP device, which is used in Australia, is the therapist-made bubble-PEP which is constructed from a container filled with water and tubing inserted into the container through which the patient expires. However, little is known about the physical properties of the bubble-PEP device or its effect on sputum clearance in patient populations. This PhD investigated: 1) the current use of the therapist-made bubble-PEP device by physiotherapists in public and private hospitals in Australia via an Australian-wide survey; 2) the pressures and oscillation frequencies generated by the therapist-made bubble-PEP device with variable air flows and tubing internal diameters via a benchtop laboratory study; 3) the pressures and oscillation frequencies generated by two versions of the therapist-made bubble-PEP devices compared to three commercially available bubble-PEP devices, via a benchtop laboratory study; and 4) whether the therapist made bubble-PEP device improved secretion clearance in people with bronchiectasis, when compared to the active cycle of breathing technique (an established ACT) or no intervention (control) in a randomised cross-over trial.