Inflammatory bowel disease (IBD) is a chronic, idiopathic inflammatory disease of gastrointestinal tract with waxing and waning clinical course, which may lead to irreversible bowel damage and a loss of bowel function. Cumulative intestinal damage results in complications such as stricture or fistulae, and eventually a large number of IBD patients undergo surgery. Notably, even during remission period (no clinical symptoms), subclinical inflammation often persists and the disease continues to progress. Therefore, the therapeutic target of IBD has been evolving from symptomatic control to mucosal healing to prevent structural intestinal damage. To achieve therapeutic goals in IBD, it is important to optimize therapy according to disease severity and response to treatment. Therefore, monitoring disease activity is recommended throughout the disease course of IBD. Especially strategies to monitor disease beyond symptoms through endoscopy, laboratory markers, and imaging is required. (Korean J Gastroenterol 2018;71:69-73)