Diarrhoea is a clinical symptom characterised by an increase in the volume, wateriness, or frequency of bowel movements. Acute diarrhoea is a common cause of death in developing countries and the second most common cause of infant deaths world-wide. The loss of fluids through diarrhoea can cause severe dehydration which is one cause of death in diarrhoea sufferers. The causes of diarrhoea can be infectious or non-infectious. Infectious causes are due to bacteria, viruses, or parasites. This book presents research on diarrheal viruses; cholera in Africa; the pathogenesis of Clostridium-difficile associated diarrhea; faecal organic anions in calf diarrhoea and the pathophysiology of irritable bowel syndrome with diarrhoea.