Tree improvement is necessary to meet the growing demand for the renewable resource wood. Many novel possibilities to obtain improved species are offered by biotechnology, and the time is ripe for a critical evaluation of the chances and challenges of tree transgenesis. Sixteen chapters by experts in the field provide concise information on the present state of the following topics: transgenic trees in the world; 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; disease resistance; drought tolerance. In addition, biosafety and risk assessment are treated in detail, and future experimental tasks are discussed. The book provides a sound basis for decision-making processes in politics.