Heterobasidion annosum (Fr.) Bref. sensu lato (s.l.) is a dangerous forest pathogen causing root and butt rot disease in most conifers of the northern hemisphere. This pathogen is most widespread in the forests of Europe and North America. The economic impact on forestry related to tree mortality, reduction in timber yield, and wood rot is calculated in millions of dollars and euros. The genus Heterobasidion (Basidiomycota; Russulales) has been relatively recently separated into three genetically distinct groups (H. annosum, H. insulare and H. araucariae) comprising a total of 12 species and one newly described hybrid taxon. These species are the best studied in terms of the ecology, the physiology of control methods, and the tree’s resistance to the pathogen. The article gives an overview of the symptoms and the etiology of the disease and provides information on ways to recognize the disease and limit the economic damage.