Lactococci are used for the manufacture of fermented dairy products. Many technological functions are coded on plasmids: lactose and citrate utilization, a cell wall associated protease, bacteriocin and slime production and phage insensitivity phenomena. Natural and artificial methods of gene transfer are available: transduction, conjugation, protoplast fusion, transformation, transfection and electroporation. Plasmid vectors for homologous and heterologous gene cloning, transfer and expression have been developed. Cloned und expressed genes include: phospho‐ß‐galactosidase, sucrose‐6‐P hydrolase, citrate permease, alpha‐acetolactate decarboxylase, bacteriophage resistance, bacteriocin production and immunity, bacteriophage lysin, cell wall protease, ß‐galactosidase fromEscherichia coli,bovine prochymosin and egg white lysozyme. The application of genetically modifiedLactococcusconstructs needs careful evaluation regarding biological safety and containment issues.