**1. Introduction**

Crohn's disease (CD) is an idiopathic inflammatory disorder with genetic, immunologic and environmental influences [1]. It is characterized by a transmural inflammation that may involve any portion of the luminal gastrointestinal tract, from the oral cavity to the perianal area. The diagnosis is based on the combination of clinical, biochemical, radiological, endoscopic and histological findings. CD is a chronic and progressive disease, marked by frequent relapses which usually require repeated investigations.

The most common symptoms of CD are diarrhea, abdominal pain and fatigue. However, clinical manifestations can be very heterogeneous, depending on the disease location and phenotype. Patients with CD often show laboratory evidence of inflammatory activity and anemia. In addition, fecal calprotectin and serum C-reactive protein are useful markers to detect and monitor inflammation. The endoscopic hallmark of CD is the patchy distribution of inflammation and mucosal biopsies usually show focal inflammation (rather than diffuse), crypt distortion and/or granulomas. Finally, cross-sectional imaging techniques provide information about the bowel wall and extra-enteric soft tissues and, therefore, can better classify disease phenotype and behavior.

Endoscopy has major implications not only for the diagnosis of CD but also for treatment and follow-up. Indeed, ileocolonoscopy and upper gastrointestinal endoscopy have well-established roles in assessing disease activity and therapeutic intervention. However, the small bowel is one of the most common areas affected in patients with CD, which is often inaccessible to conventional endoscopy. In addition, at the time of diagnosis, up to 30% of patients have only small bowel involvement, especially in the young ones [2, 3]. The advent of video capsule endoscopy and both balloon-assisted and spiral enteroscopy is revolutionizing the management of small bowel CD [4]. In fact, these techniques allowed direct visualization of the entire small bowel which can assist in the diagnosis of CD. Moreover, device-assisted enteroscopy enables direct tissue sampling and allows therapeutic interventions. In this chapter, we aim to review the role of small bowel endoscopy in the management of patients with CD.
