Comparative wood anatomy consists of two main efforts: wood identification and evolutionary studies. Evolutionary studies can be divided into two main areas: systematic wood anatomy and ecological wood anatomy. The goal of wood identification is the association of a name with a sample; that of systematic wood anatomy is the discovery of the nested hierarchy of synapomorphies that characterize the phylogeny of the woody plants; the main thrust of ecological wood anatomy has been to identify structure- function relationships that have evolved repeatedly across clades. Wood anatomical characters can be divided into three types: typological, homologous, and homoplasious. Wood identification can and should use all three types; systematic wood anatomy must focus on homologies; homologies may be of interest to ecological wood anatomy, but homoplasies have been its principal focus. The use of typological characters developed for wood identification can produce misleading results in studies of evolutionary wood anatomy and must be avoided. Robust phylogenies are important for discovering wood anatomical homologies and homoplasies; also important is the need to make explicit, testable hypotheses, and to identify the type of causation (ultimate or proximate) that is of interest for a given study.