Acute exacerbations of asthma are very common reasons for a presentation to emergency departments. This paper focuses on defining the high-risk group, consideration of the concept of phenotypes of acute asthma, the assessment of severe and life-threatening exacerbations and an emphasis on the management of the more severe end of the exacerbation severity. A number of evidence-based guidelines exist throughout the world and are all slightly different. This reflects the poor evidence base for some of those recommendations. Thus, a large variation of treatment drugs, doses and regimen are used and clearly not standardised. This paper aims to present a summary of the best evidence and discuss some of these controversies. The most important aspect of treating an exacerbation of acute asthma is to review regularly and assess response to treatment. Severe and life-threatening episodes should be treated with early use of intravenous treatment in a stepwise manner following the local guidelines. Non-invasive ventilation and high flow nasal cannulae delivery of oxygen in the emergency department are evolving modalities, but evidence for their use is currently limited.