Over the past 20 years, DNA-based biotechnologies have been applied to agricultural production and many crops with new and useful attributes have been cultivated in various countries. The adoption of this new technology by farmers has been swift, and benefits in terms of increased production per unit land and environmental benefits are becoming obvious. In forestry, the application of biotechnology is somewhat lagging behind and to date there are no commercial plantations with genetically modified trees. However, most tree species used in plantation forestry have been genetically transformed, and results demonstrate the successful and correct expression of new genes in these plants. At the same time, this new technology is being viewed with concern, very similar to the concerns voiced over the use of genetic engineering in agriculture. This paper discusses some of the issues involved for world forestry, with particular focus on future demand for timber and timber products and how modern biotechnology can contribute to meet the growing demand. Tree genetic engineering techniques will be outlined, and results reviewed for a number of species. Concerns over the use of this new technology will be described and analyzed in relation to scientific considerations.