This chapter provides general information on tree properties and wood material. It presents tree-related data, such as bark, needle, and wood biomass content and its changes over time. This chapter also gives special attention to the moisture content of the tree (in the green state) and the wood in use. On the microstructural scale of wood, data for the microfibril orientation in the cell wall, cell dimensions and proportion of the total number of cells, and some strength values of earlywood and latewood are presented. Moisture is more or less omnipresent in wood since water molecules within the wood material interact with the surrounding air and its specific climate (Use Classes). How this influences the use of sawn timber and wood-based materials, as well as the risks of wood decay, building behaviour, etc., is discussed.