“Difficult asthma” means very different things to different people. As Abisheganaden and Boushey point out in the first chapter, asthma is by definition “difficult” if you happen to suffer from it. The remainder of this multiauthor text focuses on another perspective—that of the clinician-scientist—and on asthma that is difficult for that person to manage. This is a good time for such a book. Research over the past two decades has placed inflammation at the centre of our understanding of the pathophysiology of the disease, and a new class of antiasthma drug, the antileukotrienes, is now available and is expected to find a major role in treatment.