An estimated 8.2 percent of the United States population has asthma including 9.6 percent of children and 7.7 percent of adults. In 2010, the Agency for Healthcare Research and Quality commissioned the Oregon Evidence-based Practice Center to conduct a comparative effectiveness review (CER) on the effectiveness of breathing exercises and/or retraining in the treatment of asthma. Alternative and complementary treatment methods such as breathing retraining techniques have been advocated for the control of asthma given the range of asthma severity and concerns about long-term medication use. Specific breathing retraining approaches include those related to hyperventilation reduction (e.g., the Buteyko and Papworth methods) or nonhyperventilation-targeted methods (e.g., yoga breathing techniques, other physical therapy methods, biofeedback, and inspiratory muscle training IMT]). These methods are assumed to be adjunctive to guideline-based care, with the primary goals of improving asthma control and reducing the use of medication. 1. Does the use of breathing exercises and/or retraining techniques improve health outcomes, including: symptoms (e.g., cough, wheezing, dyspnea); health-related quality of life (general and/or asthma-specific); acute asthma exacerbations; reduced use of quick-relief medications or reduced use of long-term control medications, when compared with usual care and/or other breathing techniques alone or in combination with other intervention strategies? In this review, we addressed the following Key Questions: 2. Does the use of breathing exercises and/or retraining techniques improve pulmonary function or other similar intermediate outcomes when compared with usual care and/or other breathing techniques alone or in combination with other intervention strategies? 3. What is the nature and frequency of serious adverse effects of treatment with breathing exercises and/or retraining techniques, including increased frequency of acute asthma exacerbations? Our review sought to include studies that addressed the use of breathing techniques in adults and children 5 years of age and older with asthma and explored whether the effectiveness differed between different population subgroups (e.g., males/females; various types and severities of asthma; and/or different coexisting conditions). Additionally, we evaluated whether the effectiveness of these interventions varied by differences in intervention implementation or components. The review identified 22 studies published between 1990 and December 2011 that examined the effectiveness or comparative effectiveness of breathing techniques on intermediate and/or health outcomes. In general, the evidence was low-to-moderate or insufficient to address the Key Questions adequately as it was based primarily on small, methodologically limited trials of heterogeneous populations with short followup and inconsistent outcome reporting. The objective of this Future Research Needs project was to engage a diverse set of stakeholders to confirm, provide more detail, and prioritize the research needs that we identified in the CER. We also sought to provide information on ongoing studies of relevance to the prioritized list of research questions and study design considerations for the highly prioritized questions.