Eosinophilic oesophagitis (EoE) has first been described a little over 20 years ago. EoE has been defined by a panel of international experts as a "chronic, immune/antigen-mediated, oesophageal disease, characterized clinically by symptoms related to oesophageal dysfunction and histologically by eosinophil-predominant inflammation". A value of ≥ 15 eosinophils has been defined as histologic diagnostic cutoff. Other conditions associated with oesophageal eosinophilia, such as gastro-oesophageal reflux disease (GERD), PPI-responsive oesophageal eosinophilia, or Crohn's disease should be excluded before EoE can be diagnosed. This review highlights the latest insights regarding the diagnosis and differential diagnosis of EoE.