This is a survey of well characterized and recently discovered bacterial protein toxins. Leading investigators of the respective toxins review the various molecular mechanisms of action, ranging from toxin-induced ADP-ribosylation up to membrane perforation by pore-forming toxins. Thy also describe the consequences on host physiology before focusing on potential applications as cell biological and pharmacological tools for research and medical applications. Detailed descriptions of the methodology include the engineering and use of modified and chimeric toxins for better performance. A solid introduction to toxin structure and functions, as well as a valuable source of methodology for researchers in molecular biology, pharmacology and experimental medicine.