Background: People with bronchiectasis experience chronic cough and sputum production and require the prescription of airway clearance techniques (ACTs). A common type of ACT prescribed is positive expiratory pressure (PEP) therapy. A previous review has suggested that ACTs including PEP therapy are beneficial compared to no treatment in people with bronchiectasis. However, the efficacy of PEP therapy in a stable clinical state or during an acute exacerbation compared to other ACTs in bronchiectasis is unknown. Objectives: The primary aim of this review was to determine the effects of PEP therapy compared with other ACTs on health-related quality of life (HRQOL), rate of acute exacerbations, and incidence of hospitalisation in individuals with stable or an acute exacerbation of bronchiectasis. Secondary aims included determining the effects of PEP therapy upon physiological outcomes and clinical signs and symptoms compared with other ACTs in individuals with stable or an acute exacerbation of bronchiectasis. Search methods: We searched the Cochrane Airways Group Specialised Register of Trials, PEDro and clinical trials registries from inception to February 2017 and we handsearched relevant journals. Selection criteria: Randomised controlled parallel and cross-over trials that compared PEP therapy versus other ACTs in participants with bronchiectasis. Data collection and analysis: We used standard methodological procedures as outlined by Cochrane. Main results: Nine studies involving 213 participants met the inclusion criteria, of which seven were cross-over in design. All studies included adults with bronchiectasis, with eight including participants in a stable clinical state and one including participants experiencing an acute exacerbation. Eight studies used oscillatory PEP therapy, using either a Flutter or Acapella device and one study used Minimal PEP therapy. The comparison intervention differed between studies. The methodological quality of studies was poor, with cross-over studies including suboptimal or no washout period, and a lack of blinding of participants, therapists or personnel for outcome measure assessment in most studies. Clinical heterogeneity between studies limited meta-analysis. Daily use of oscillatory PEP therapy for four weeks was associated with improved general health according to the Short-Form 36 questionnaire compared to the active cycle of breathing technique (ACBT). When applied for three sessions over one week, minimal PEP therapy resulted in similar improvement in cough-related quality of life as autogenic drainage (AD) and L'expiration Lente Totale Glotte Ouverte en Decubitus Lateral (ELTGOL). Oscillatory PEP therapy twice daily for four weeks had similar effects on disease-specific HRQOL (MD -0.09, 95% CI -0.37 to 0.19; low-quality evidence). Data were not available to determine the incidence of hospitalisation or rate of exacerbation in clinically stable participants. Two studies of a single session comparison of oscillatory PEP therapy and gravity-assisted drainage (GAD) with ACBT had contrasting findings. One study found a similar sputum weight produced with both techniques (SMD 0.54g (-0.38 to 1.46; 20 participants); the other found greater sputum expectoration with GAD and ACBT (SMD 5.6 g (95% CI 2.91 to 8.29: 36 participants). There was no difference in sputum weight yielded between oscillatory PEP therapy and ACBT with GAD when applied daily for four weeks or during an acute exacerbation. Although a single session of oscillatory PEP therapy was associated with less sputum compared to AD (median difference 3.1 g (95% CI 1.5 to 4.8 g; one study, 31 participants), no difference between oscillatory PEP therapy and seated ACBT was evident. PEP therapy had a similar effect on dynamic and static measures of lung volumes and gas exchange as all other ACTs. A single session of oscillatory PEP therapy (Flutter) generated a similar level of fatigue as ACBT with GAD, but greater fatigue was noted with oscillatory PEP therapy compared to ACBT alone. The degree of breathlessness experienced with PEP therapy did not differ from other techniques. Among studies exploring adverse events, only one study reported nausea with use of oscillatory PEP therapy. Authors' conclusions: PEP therapy appears to have similar effects on HRQOL, symptoms of breathlessness, sputum expectoration, and lung volumes compared to other ACTs when prescribed within a stable clinical state or during an acute exacerbation. The number of studies and the overall quality of the evidence were both low. In view of the chronic nature of bronchiectasis, additional information is needed to establish the long-term clinical effects of PEP therapy over other ACTs for outcomes that are important to people with bronchiectasis and on clinical parameters which impact on disease progression and patient morbidity in individuals with stable bronchiectasis. In addition, the role of PEP therapy during an acute exacerbation requires further exploration. This information is necessary to provide further guidance for prescription of PEP therapy for people with bronchiectasis.