A review article. The author (a member of the staff of the Forest Products Research Laboratory, Princes Risboroug England) particularly focusses attention on the physical techniques which are playing an important role in elucidating the properties of wood. These techniques include: electron micoscopy and x-ray diffraction spectroscopy for revealing micro-features of wood fibres; absorption of beta-rays to measure variation of density in wood; ultrasonic pulse techniques for measurement of elastic constants; electron micrographs for studying the movement of water or sap through pits in softwoods; porosity to bases by means of a gas-flow technique using nitrogen. Work on methods of protecting wood from insects and fungi is described. Types of insecticides are compared. Low voltage x-radiography (c. 15-25 KeV) using x-ray tubes with beryllium windows has proved useful for locating position and size of larvae. A discussion of types of wood-decay follows. As well as the higher fungi, <i>Basidiomycetes (of which dry-rot is an example), microfungi have also been studied which cause 'soft-rot' in timber in the ground. One of these micro-fungi may be responsible for ultimate failure of preservative-treated wood. Methods for chemical modification of wood are compared. It is concluded that impregnating with low viscosity materials which can be polarised with gamma-radiation is a promising method. -- AATA