This book explores the applications of third space endoscopy - an innovative application of traditional endoscopy that facilitates surgical tissue removal, intentional scar formation, or muscle division in a minimally invasive and incisionless fashion. The main topics presented include tissue removal, such as endoscopic mucosal resection (EMR), endoscopic submucosal dissection (ESD), endoscopic full-thickness resection (EFTR) and peroral tumorectomy (POET); intentional scar formation, such as anti-reflux mucosectomy (ARMs) and transoral incisionless fundoplication (TIF); and muscle division, such as peroral endoscopic myotomy (POEM) of the cricopharyngeus (ZPOEM) and pylorus (G-POEM). Despite their existence for years, many of these applications are underutilized and perhaps under-recognized by the greater medical community. Additionally, third space endoscopy spans the entire body and is performed across numerous specialties, therefore creating a single resource that encompasses all the applications in-depth will be a powerful and convenient tool for practitioners. Third Space Endoscopy is an excellent resource for medical students, residents, fellows, and attending physicians in both the surgical and gastroenterological disciplines.