Environmental problems such as global warming, acid rain, and ozone depletion are becoming increasingly serious worldwide. In order to alleviate these problems, the development of biomass that has a minimal influence on the environment has recently attracted interest as a resource that can replace fossil fuels, such as oil and coal. Wood biomass derived from forests constitutes a large part of the biomass on the earth, and wood is also the most abundant source of cellulose fibers. Therefore, the sustainable use and reproduction of wood biomass as fuel, fiber, and timber for buildings are necessary for the coexistence of human life with environmental preservation. Based on this background, the goal of this study is to elucidate the mechanisms controlling wood formation and wood properties in trees and to use this information to promote the effective use of wood materials. The fundamental constituent of the wood in a tree is the highly developed cell wall formed by xylem cells. It has been postulated that the properties of wood are closely associated with the structure of wood tissues, the properties of cell walls, and the mechanisms of cell wall formation. In addition, wood formation is strongly influenced by environmental factors, such as water, light, chemical matter, and physical forces. I have been studying the mechanisms of xylem cell wall formation and responses to the environment, as well as the effects of environmental factors on wood formation and wood properties in trees using various approaches involving the fields of histology, physiology, physics, and molecular biology. These studies should contribute to the development of trees that grow rapidly, with excellent wood quality and a good tolerance of environmental stresses, to produce usable wood materials that will help to improving and preserving the environment.