This special May issue of Clinical Endoscopy discusses the tutorial contents dealing with either the diagnostic or therapeutic gastrointestinal (GI) endoscopy that contain very fundamental and essential points in this filed. The seminar of Korean Society of Gastrointestinal Endoscopy (KSGE) had positioned as one of prime educational seminars covering the very beginner to advanced experts of GI endoscopy. Besides of four rooms allocated for each lecture, two additional rooms were open for either live demonstration or hands-on course, covering totally 20 sessions including one special lecture. Among these prestigious lectures, 12 lectures were selected for the current review articles in this special issue of Clinical Endoscopy journal. Basic course for beginner to advanced tips to expert were all covered in this seminar. This introductory review prepared by four associated editors of Clinical Endoscopy contained core contents divided into four sessions-upper gut, lower gut, pancreaticobiliary, and specialized topic session part-to enhance understandings not covered by enlisted review articles in this issue.