This volume is based on a workshop on Woody Plant Biotechnology held at the Institute of Forest Genetics, USDA Forest Service, Placerville, California, USA, 15-19 October, 1989. This workshop was organized by the IUFRO (International Union of Forestry Research Organizations) Working Party S2.04-07 - Somatic Cell Genetics -, and supported by the NATO Scientific Affairs Division, Advanced Research Workshop (ARW 692/89) Programme. This was the second workshop of the IUFRO Working Party on Somatic Cell Genetics. The first meeting of this Working Party was held at the Institute of Forest Genetics and Forest Tree Breeding, Federal Research Centre for Forestry and Forest Products, Grosshansdorf, Federal Republic of Germany. The purpose of the present workshop was to bring together scientists from different countries of the world for discussions in the area of woody plant biotechnology. Tissues from woody plants, in particular forest trees, are in general difficult to grow and differentiate in vitro. However, recent advances in tissue culture technology nave­ paved the way for successful culture of organs, tissues, cells, and protoplasts of woody plants. By employing juvenile tissues, plant regeneration has been accomplished in a number of woody plant species. On the other hand, clonal propagation of mature trees, in particular conifers, is still very difficult by tissue culture.