Biodiversity is of great importance for the functioning of the forest ecosystem. Habitat trees (Fig. 1) are a key component of forest biodiversity. Experts from Europe have developed a typology of tree-related microhabitats, small life-sites borne by some trees, which are indispensable for thousands of specialised organisms. The uniform use of the forms, groups and types of these tree-related microhabitats facilitates the implementation of recommendations in forestry practice. In addition, these standardised data can be used for monitoring forest biodiversity or for evaluating the success of measures to promote biodiversity in forests.