The "third space endoscopy" or also called "submucosal endoscopy" is a reality we can transfer to our patients since 2010. Various modifications of the submucosal tunneling technique allow access to the submucosa or deeper layers of the gastrointestinal tract. In addition to peroral endoscopic myotomy for the treatment of achalasia, also called esophageal POEM, other variants have emerged that make it possible to treat different esophageal motility disorders, esophageal diverticula, subepithelial tumors of various locations, gastroparesis, reconnection of complete esophageal strictures or even thanks to exceptional endoscopists, pediatric disorders such as Hirschsprung's disease. Although some technical aspects are yet to be standardized, these procedures are becoming widespread worldwide and will likely become the standard treatment of these pathologies soon.