Respiratory diseases, including allergies, asthma and chronic obstructive pulmonary disease, are a major public health burden worldwide.The latest WHO statistics (2007) estimate that 300 million people worldwide have asthma, 210 million people have this type of pulmonary disease, and millions of people are affected by allergies. Each year, 250,000 people die of asthma. The prevalence of these diseases is increasing, and there is a continued need for new and improved therapies. A March 2008 Focus issue of Nature Reviews Immunology highlights the latest advances in our understanding of the immune bases of these respiratory diseases and how this knowledge can be translated into effective treatment strategies, in five review articles and four research highlights. All Focus articles are freely available online for the month of March.