An increasing number of children and adults are currently suffering symptoms due to FODMAP (Fermentable Oligosaccharides, Disaccharides, Monosaccharides and Polyols) consumption. These carbohydrates are poorly digested in the human gastrointestinal tract, exerting an osmotic effect in the small intestine. In the colon, they become substrates to the microbiota. Microbial fermentation explains symptoms such as abdominal distention (postprandial fullness), bloating and flatulence, abdominal pain and loose feces or diarrhea. There are no standardized methods to measure them in daily clinical work. Daily tolerance and the no-effect doses are unclear. How to diagnose and treat FODMAP associated symptoms is also controversial. In this review, we aim to define FODMAP, their associated symptoms and the current techniques for assessing them. The low-FODMAP diet is described and how to implement it.