Adherence in asthma is an important cause for concern. Although nearly 50% of asthma patients are considered poorly adherent to therapeutic advices, adherence is still difficult to assess, understand and improve despite major medical consequences. In this review, we revisited the literature of the last 10 years related to adherence in severe asthma. The concepts have changed and “compliance” is usually replaced by “adherence”. Assessment of adherence is addressing ethical issues, but provides important insight into difficult-to-treat asthma. Different tools have been used but none is routinely recommended. Health-related outcomes (poor control, exacerbations, hospitalizations, lung function decline), which are clearly associated with severe asthma, are often worsened by non-adherence with consequences also on patient related outcomes (quality of life). The potential behaviour associated with non-adherence and all other related factors including easy-to-recognize psychological traits can help for patient's future management. Therapeutic educational interventions have been recognized with a scientifically proven efficiency even though evolution and improvements are needed. A multidisciplinary approach is required in severe asthma. Therapeutic adherence for a given patient is always a prerequisite to any other aspects when addressing severe asthma phenotypes. Severe asthma should be considered only in those who still experienced poor asthma outcomes despite optimal adherence. At a glance, poor adherence and severe asthma should be considered antinomic. Better understanding of the causes and customised management are potential future directions.