The present paper is a revised edition of former Document No: IRG/WP/125. It contains some additions and an explanation of terminology, as was suggested at a previous meeting of the Group. The paper is a compilation based mainly on available literature. Some of my own unpublished results have been added together with other unpublished data which have been received from the Bundesanstalt für Materialprüfung in Berlin and from colleagues at the Department of Forest Products, Swedish University of Agricultural Sciences, which are acknowledged with thanks. Fungi, described in the text, have been selected according to the following principles: a) the most common and important blue stain fungi, b) less common fungi which have been found in several countries or on several host trees, c) fungi which seem to be of minor interest as blue stain fungi, but which have been used recently in experimental work considering their physiological characters, susceptibility for toxic substances etc. The author regrets that this paper does not cover the tropical fungi, as there have been only a few notes about these in reviews and as the original papers have not been available to our library.