The subject of preservation is a wide one and cannot be covered adequately in one lecture. There has been considerable progress in the development of better methods of treatment and new types of preservatives during the past few years. Further research is needed to discover why some timbers are very readily treatable while others are untreatable, and why different pieces of the same timber, even when from the same tree, do not react in the same way under treatment. Research is being fostered by the British Wood Preserving Association, a non-trading association aiming at the more efficient use of timber by prolonging its service life. The Association maintains a free advisory service and publishes leaflets on various aspects of preservation which are supplied free of charge to anyone needing information.