Clostridia have a high biotechnological potential, although they are generally still regarded more as a group of pathogenic microorganisms. They undertake a broad variety of biocatalytic reactions some of which are unique and of use in the chemical and biotechnology industry for the production of chemicals or for biopharmaceutical purposes. Even some of the clostridial toxins are of medical relevance and can be used as therapeutic agents; The book presents the biology, pyhsiology, and genetics, including genome projects of Clostridia and highlights their potential for industrial and medical applications. It is mostly based on research during the last decade which has brought significant progress in the field and outlines future perspectives of industrial interest.