Creating bacteria with modified genetic properties allows the specific investigation of these microorganisms. Electrotransformation is a highly efficient and easy to apply technique to introduce genetic material into bacterial cells. A strong electric field is used for this purpose. In the present manual, protocols for the transformation of about 40 strains of bacteria are described. Emphasis is placed on the individual critical procedural steps, since the practical details mainly depend on the bacterial strain under investigation. This presentation together with the theoretical introductionary chapters, allows the user to modify and adapt each protocol to his/her own experiments. Bacterial strains with relevance in the food industry, biotechnology, medical and veterinary fields, agroindustry and environmental sciences are covered.