The landscape of modern endoscopy has undergone a profound transformation with the introduction and increasing prominence of advanced interventions in the third space, notably exemplified by Endoscopic Submucosal Dissection (ESD), Peroral Endoscopic Myotomy (POEM) and Submucosal Tunneling Endoscopic Resection (STER). They demand an unparalleled level of precision and understanding of tissue dynamics, challenging the conventions of endoscopic practice. Despite their growing adoption, a noticeable gap exists in evidence-based curricula and standardized training protocols, underscoring the need for a focused exploration of training methodologies. The imperative for proficient endoscopists capable of navigating the intricacies of anatomical layers has become increasingly paramount.

As for ESD, a training curriculum by the European Society of Gastrointestinal Endoscopy[1] is already in place and would exceed the limitations of this review; therefore, this synthesis will primarily focus on other third-space endoscopies (TSE), especially POEM.

Since the invention of ESD in the 1990s in Japan, many novel techniques exploring the second (peritoneum) and third space have been developed. The invention of the mucosal flap safety valve enabled endoscopists to access the third space with a rapidly decreasing complication rate[2]. Ranging from the treatment of motility disorders over Zenker's diverticulum to subepithelial tumors, esophageal recanalization (POETRE), and even mediastinal tumor or gallbladder removals3, 4, 5, there seems to be no limit to the boundaries of modern endoscopy. But how does one become an adept endoscopist and initiate performing these procedures? This review comprehensively explores multifaceted training methodologies, encompassing simulators, preclinical models, and clinical training.