Many misconceptions exist regarding the deterioration, restoration and care of wood. Because of this the basic biological and physical properties of wood are described in order to provide a better understanding of the underlying causes of wood furniture deterioration. Among the topics included are the physical structure of trees and tree cells, the growth characteristics of trees, the three different planes of wood, figure types in wood and the strength of wood. This is the third in a 10-part series of articles on furniture conservation.