**1. Introduction**

Celiac disease (CD) is a chronic immune-mediated enteropathy triggered by exposure to dietary gluten in genetically predisposed individuals [1]. The diagnosis rate of this pathology has increased in the last 10 years [2], so worldwide epidemiologic data are now available showing that CD is ubiquitous, with a prevalence of 1.4% [3], higher in female than male individuals [2–7].

Clinically, CD presents with a wide variety of gastrointestinal and extraintestinal symptoms that differ considerably according to the age of presentation [8] or even be an asymptomatic disease. Digestive symptoms and growth retardation are frequent in the pediatric population diagnosed within the first years of life [9]. However, in adults, symptoms can be nonspecific gastrointestinal or extraintestinal of various kinds.

Currently, the only available treatment for CD is a strict, lifelong gluten-free diet (GFD), which requires significant patient education, motivation, and followup [10]. Adherence to a GFD is not easy, with the ubiquitous nature of gluten,

cross-contamination of foods, inadequate food-labeling regulations, and social constraints [11]. Current methods to evaluate adherence to a GFD include the use of a dietary questionnaire and monitoring of serological findings or clinical symptoms; however, neither of these methods generates a direct nor an accurate measurement of dietary adherence [1, 11, 12]. Small bowel biopsy is the "gold standard" for CD diagnosis, but according to most clinical guidelines, its role in the follow-up of patients with CD is limited to cases involving a lack of clinical response or symptom recurrence [13–17]. Nonresponsive CD occurs frequently, particularly in those diagnosed in adulthood. Persistent or recurring symptoms should lead to a review of patients to exclude alternative diagnoses and a review of GFD to ensure there is no obvious gluten contamination and confirm adherence to GFD [1]. Possible causes include age at diagnosis, follow-up time, the existence of social differences, the intake of certain drugs (PPIs, NSAIDs), severe clinical symptoms at diagnosis, inadequate adherence to diet, or the presence of inadvertent contamination of the diet [18, 19].

In this chapter, we synthesized the latest research findings and evidence related to the management of CD and GFD, including emerging tools to monitor the correct adherence to GFD and the development of non-dietary therapies.
