A detailed review of the wood fatigue literature is presented and the need for experimental work under load control at a range of moisture contents and Rratios is emphasized. A laminated hardwood, Khaya ivorensis, a softwood, Sitka spruce, and compressed beech laminates were fatigue tested under load control in four point flexure. Tests were conducted in repeated and reversed loading over a range of five Rratios at three moisture contents, and the accumulation of fatigue damage was followed by microtoming fatigued wood and observing the formation of cell wall kinks by polarized light optical microscopy. Fatigue life is largely species independent when normalized by static strength. Increased moisture content reduces the static strength and fatigue life and reversed loading results in the lowest fatigue life. A constant life diagram for sliced Khaya laminate has been constructed which summarizes the effect of Rratio on fatigue life. Optical microscopy demonstrates that fatigue damage is progressive commencing on the compression face of flexural samples as fine scale cell wall kinks and developing into macroscopic creases.