1 Genus and Species Definitions 2 Historical Background of the Pathogenic Clostridia 3 Milestones in the Understanding of Botulism and Tetanus 4 Classification of Neurotoxigenic Clostridia 5 Habitats of Pathogenic Clostridia 6 Physical and Metabolic Properties of Pathogenic Clostridia including C. botulinum and C. tetani 7 Growth Properties of C. botulinum and C. tetani 8 Physiology of C. botulinum and C. tetani 9 Descriptions of the Species C. botulinum, C. tetani, and other Neurotoxigenic Clostridia 10 Botulinum Neurotoxins 11 Detection of Botulinum and Tetanus Neurotoxins 12 Genomics of Clostridium tetani and Clostridium botulinum 13 Susceptibility of Neurotoxigenic Clostridia to Chemical and Physical Agents 14 Epidemiology and Clinical Aspects 15 Use of Botulinum Toxin in Medicine 16 Safety Precautions for Working with C. botulinum, C. tetani, and their Neurotoxins 17 Acknowledgments Keywords: Clostridium botulinum and Clostridium tetani; understanding botulism and tetanus; pathogenic clostridia habitats; C. botulinum and C. tetani growth properties; botulinum neurotoxins; Clostridium tetani and Clostridium botulinum genomics; susceptibility of neurotoxigenic clostridia to chemical and physical agents; botulinum toxin use in medicine