This chapter examines the genus Clostridium, which contains many species of bacteria that cause human diseases. It analyzes how Clostridium can produce some of the deadliest toxins ever discovered and describes distinctive infections of Clostridium that includes botulism, tetanus, gas gangrene, and food poisoning from Clostridium perfringens. It also examines clostridia that are obligate, anaerobic, spore-forming bacilli and are ubiquitous in the environment, in soil and marine sediment. The chapter mentions botulism as a rare but potentially fatal disease caused by Clostridium botulinum bacteria, which produce botulinum toxin, one of the most potent bacterial toxins ever described. It talks about tetanus as a neurologic disorder characterized by muscle spasms.