Abstract: This month's theme: Asthma-COPD link About the cover Asthma and COPD are common respiratory diseases.Asthma frequently starts in childhood, and COPD starts in adulthood.Clinicians question the similarities and differences between these two diseases.This is especially important as we evaluate the diagnosis in adults and seek to manage each disease.Although some of the medications used for COPD and asthma are similar, there are some unique differences due to the pathology and clinical response to therapy.This month's theme is centered on differences in asthma and COPD.In a Clinical Reviews article, Brendan J. Carolan and E. Rand Sutherland (p 627) discuss recent advances in understanding clinical phenotypes of COPD in relation to asthma.They conclude that it is likely that further elucidating the heterogeneity of COPD and asthma through clinical and biologic phenotyping will allow greater understanding of pathogenetic mechanisms and for more directed management, especially when patients are not controlled with first-line modalities.As part of our Mechanisms of Allergic Diseases series, Peter J. Barnes (p 636) discusses corticosteroid resistance in asthma and COPD.He indicates that identifying the molecular mechanisms of steroid resistance in asthma and COPD may lead to more effective anti-inflammatory treatments in the future.This month's cover image points out some of the differences in pathophysiology between asthma and COPD.