This review summarises the results of preclinical studies aimed at elucidating the mode of action of alendronate and assessing its effects on bone quality. Alendronate preferentially localises at bone resorption sites, where the drug inhibits osteoclastic activity. In a variety of estrogen-deficient animal models, alendronate normalised bone turnover, promoted normal mineralisation and increased bone mass and strength. In these studies, bone formed during alendronate therapy was histologically normal and was not associated with spontaneous fractures. Therefore, preclinical studies have established that the antiresorptive activity of alendronate results in the prevention of bone loss and the accretion of normal-quality bone.