This document provides an overview of acute gastroenteritis. It defines acute diarrhea and lists common causes in both adults and children, including viral, bacterial, and parasitic infections as well as some non-infectious conditions. The document outlines the clinical approach to a patient with acute diarrhea including taking a thorough history and physical exam. It notes key indications for testing stool or blood. The management section discusses rehydration therapy including oral rehydration solutions, diet, use of anti-diarrheal medications, antimicrobial therapy, and probiotics.