Mass poisoning is characterized by occurrence of similar symptoms in previously healthy people in a narrow time frame. A toxic agent as cause for the health impairment is often not identified during the early stage, especially if oral exposure is causing the mass poisoning. The toxicity of sources can be inherent to the agent itself (e.g. toxic fungi, ethanol and recreational drugs) or be the result of contamination (e.g. toxins from microorganisms or nitrate in food, heavy metals in drinking water). Most mass poisonings are unintended. However, there have also been many incidents reported in the past where mass poisoning was the result of intentional action. Examples are the debasement of food, falsification of alcoholic beverages with methanol, medical drug fraud or “stretching” of drugs with agents showing higher toxicity than the drug itself. The chapter gives an overview of typical and extraordinary scenarios and describes the most important aspects of treatment of mass poisoning, mainly caused by oral exposures.