AbtractBeech bark disease is an often lethal malady ofFagus sylvaticaandF.grandifolia. Observations in North America and recent studies in Great Britain and France support the concept that the disease complex occurs when bark, infested by the scale insectCryptococcus fagi, is infected and killed by fungi of the genusNectria. Comparisons of the ecology of beech bark disease, borne out by recent investigations in North America, Great Britain, France and Germany, are presented.