Asthma is a common chronic disease with underlying inflammation of the airway. Advances in science have led to increased understanding of the heterogeneous nature of asthma and its complex mechanisms. Traditionally, asthma-practice guidelines have focused on optimizing lung function and the US FDA has required increases in lung function and reduction of exacerbation as primary outcomes in clinical trials of new asthma therapeutics. Improved lung function is a critical indicator of bronchodilator therapy, but the importance of long-term asthma control while maintained on controller medication is increasingly emphasized. The NIH asthma guidelines suggest the use of patient-reported outcomes, including health-related quality-of-life measures, to assess asthma control. Clinical practices and research studies concerning asthma can benefit from harmonizing the major outcome measures so that comparisons across studies can be made. In this article, we review common asthma outcome measures with a focus on recent efforts to harmonize outcomes for therapeutic clinical trials in asthma.