This chapter introduced the GI system, which is essential for optimal nutrition, health, and wellness of the human body. The complex processes of ingestion, digestion, absorption, and metabolism require properly functioning GI structures. The overall process was described, from mastication of food through evacuation of stool. The chapter explained how dysfunction or physical deficits can lead to GI problems, which may be mild and temporary or may result in chronic and even life-threatening conditions. Medications are often essential to promote a healthy, functioning GI system and to augment nutrition.