There are many different biological, chemical, or radiological agents that when added to food can result in many different types of illness. Some may be rapidly fatal; others require long-term exposure to result in illness. Some lead to short-term illness and others result in long-term complications. The universe of such agents and situations is enormous. This article summarizes some of the principal foodborne microbiological agents that clinicians and those involved with public health have to deal with. While the range of agents is broad and the list is long there are several basic mechanisms such as ingestion of preformed toxins or toxin production once a microbe is present in the intestine that facilitate sorting these agents into some logical framework. However, at the end of the day it is always key to think about ingested agents as a cause for illness, whether that illness be confined to the intestinal system or more systemic. In principle all foodborne illness is preventable and of the key messages to consumers and health care professionals is to know if you or your patient is at greater risk from foodborne illness. If one is dealing with an ‘at risk’ patient, it is important they be educated on what foods to avoid and what precautions to take to minimize the likelihood of acquiring a foodborne illness. While treating most foodborne illness is straightforward, prevention is clearly the path of choice.