Eosinophilic oesophagitis is an increasingly recognized allergic gastrointestinal disease, which is becoming more common. Although the average age at diagnosis is 30–50 years, it often affects very young children and carries significant long-term morbidity. While our understanding of its pathophysiology is accumulating, the precise pathways by which the disease arises remain unclear. There are inconsistencies in its diagnosis and definition, and a drive towards international standardization is underway. Current methods for diagnosis and monitoring are relatively invasive, and controversies surround their interpretation. Management strategies are imperfect and involve burdensome long-term dietary exclusions, or drug treatments with uncertain efficacy or serious side-effects. It is the focus of a rapidly increasing body of research, the latest insights from which are systematically presented in this review.