Oak woods phenolics, extractives and cell wall linked compounds: lignins, lignans, tanins and phenolic aldehydes have been discussed, at the molecular level, in their relations with physico-chemical properties of wood = shrinking, permeability and mechanical properties. Unpublished results have been also reported concerning fractionnation of cell wall phenolics, incrustation of cell wall by tanins: ellagic acid associated with lignins fractions and formation of phenolic aldehydes (vanillin, syringaldéhyde, coniferaldehyde, sinapaldehyde) during mild pyrolysis of lignin in oak wood. Hypotherical reaction mechanism have been suggested.