Toxins can be defined by many ways on basis of origin, chemical nature and site of actions. Any microbial product, when present at low concentration in cells or tissues of a higher organism, can cause injury by interfering with the structural and functional integrity of those cells or tissues. Toxins are produced by bacteria, fungi, algae and various other micro-organisms. This review will put some light on various types of microbial toxins their structure and function and how they affect the human body. The book is of benefit to all the students of microbiology, biochemistry medical science, biotechnology and to all individuals interested in the subject.