Achalasia is a rare motility disorder with incomplete relaxation of the lower esophageal sphincter and ineffective contractions of the esophageal body. It has been hypothesized that achalasia does not result from only one pathway but rather involves a combination of infectious, autoimmune, and familial etiological components. On the basis of other observations, a novel hypothesis suggests that a muscular form of eosinophilic esophagitis is involved in the pathophysiology of achalasia in some patients. This appears to progressively diminish the myenteric plexus at stage III, gradually destroy it at stage II, and finally eliminate it at stage I, the most advanced and final stage of achalasia. Although high-resolution manometry has identified these three different types of achalasia, another subset of patients with a normal-appearing sphincter relaxation has been proposed. Provocative maneuvers, such as the rapid drinking challenge, have recently been demonstrated to improve diagnosis in certain borderline patients, but have to be studied in more detail. However, whether the different types of achalasia will have a long-term impact on tailored therapies is still a matter of debate. Additionally, novel aspects of the standard timed barium swallow appear to be an important adjunct of diagnosis, as it has been shown to have a diagnostic as well as a predictive value.© 2020 New York Academy of Sciences.