This chapter discusses the normal structure and disorders of the gastrointestinal tract. The oesophagus is a muscular tube extending from the pharynx to the stomach. The wall of the oesophagus consists of mucosa, submucosa, muscularis propria and adventitia/serosa. The mucosa is composed of non-keratinising stratified squamous epithelium overlying lamina propria except at the lower end. The submucosa consists of loose connective tissue with sprinkling of lymphocytes, plasma cells, and occasional eosinophil and mast cell. Congenital atresia of the oesophagus is associated with tracheo-oesophageal fistula, usually at the level of tracheal bifurcation. The condition is characterized by regurgitation of every feed, hypersalivation, attacks of cough and cyanosis. Achalasia of the oesophagus is a neuromuscular dysfunction due to which the cardiac sphincter fails to relax during swallowing and results in progressive dysphagia and dilatation of the oesophagus. Hiatus hernia is the herniation or protrusion of part of the stomach through the oesophageal hiatus of the diaphragm. Diverticula are the outpouchings of oesophageal wall at the point of weakness. They may be congenital or acquired. Massive haematemesis (vomiting of blood) may occur due to vascular lesions in the oesophagus. Reflux of the gastric juice is the commonest cause of oesophagitis.