Transgenic Trees in the World -- Field Trials with Transgenic Trees - State of the Art and Developments -- Transgenic Forest Trees in China -- Modification of Perennial Fruit Trees -- Genetic Transformation of Some Tropical Trees, Shrubs, and Tree-like Plants -- Wood and other Traits -- Environmental Aspects of Lignin Modified Trees -- Modification of Cellulose in Wood -- Heavy Metal Resistance and Phytoremediation with Transgenic Trees -- Transgenic Approaches to Engineer Nitrogen Metabolism -- Biotic and Abiotic Resistances -- Virus Resistance Breeding in Fruit Trees -- The Use of Genetic Transformation Procedures to Study the Defence and Disease Resistance Traits of Trees -- Fungal and Bacterial Resistance in Transgenic Trees -- Genetically Modified Trees Expressing Genes for Insect Pest Resistance -- Towards Genetic Engineering for Drought Tolerance in Trees -- Biosafety Issues -- Genome Instability in Woody Plants Derived from Genetic Engineering -- Investigation of Horizontal Gene Transfer from Transgenic Aspen to Ectomycorrhizal Fungi -- Transgenic Temperate Fruit Tree Rootstocks. A continuous development in plant biotechnology including gene technology has been observable during the past 20 years. Different methods elaborated with model plants were also applied to forest trees on a larger scale. Whereas in the beginning the meaning of the term "plant biotechnology" embraced a wide variety of meanings like, e. g. , regeneration of plantlets via tissue culture, embryo rescue, somatic embryogenesis and gene transfer, the focus of this term has changed more and more. Nowadays, it is the transfer of genes which comes into mind when plant biotechnology is discussed, including of course the evaluation of all challenges and risks related to gene transfer methods. Compared with annual plants, especially in the field of agriculture, the work and the progress with transgenic trees is still in its infancy. Nevertheless, but often unnoticed by the scientific community, there are a few countries which already allow the commercial use of a restricted number of transgenic tree clones after different critical steps of approval. This and the ongoing improvement in transgenic research in trees led to the idea of preparing a summary of the present state of the art from different points of view. With the help of a number of authors directly or indirectly involved in tree transgenesis, this book was produced.