In forestry, genetic engineering is used to produce new varieties of trees which have valuable traits such as increased herbicide-tolerance, pathogen- and herbivore-resistance and high quality of wood. The developed research methods consisting of gene-engineering and transformation of the forest tree species via Agrobacterium tumefaciens or particle bombardment techniques opened a new field in forest genetics. Genetic modification as well as conventional breeding techniques seek for genetic improvement of forest tree species in order to make them more productive under certain environmental conditions. In contrast to traditional breeding based on natural variation of plant phenotype, in genetic modification technologies the genes controlling desired traits are isolated, their DNA sequences are determined, and recombinant genes are reintroduced into plant cells. Plantations of genetically modified trees require some environmental protection measures in order to prevent any cross-pollination in open field. Possible benefits of transgenic trees are associated with increasing economic efficiency of forestry, and they can provide important environmental benefit such as reduced use of pesticides or less pressure on native forests as wood, fibre and energy suplier.