A tree-related microhabitat (abbreviated as TreM) is a morphological feature present on a tree, which is used by sometimes highly specialised species during at least one part of their life cycle. These features may serve as shelters, breeding spots, or crucial hibernation or feeding places for thousands of species. Each TreM provides very specific conditions to the inhabiting species, depending on its characteristics, such as size, shape, position in the tree, degree of decomposition of the surrounding wood, condition of the bearing tree (living or dead), exposure to sunlight, microclimate, and moisture content. The diversity of TreMs in a forest stand directly influences the diversity of species because different TreMs provide optimal conditions for various species to thrive. To reinforce biodiversity in a stand and thus improve its resilience, we need to know which TreMs are present, and to preserve and favour them through adapted management practices. This field guide describes 52 TreMs in boreal and hemiboreal forests. These microhabitats can be categorised into 17 groups, with these groups falling within 7 overarching forms. The guide also indicates recommended minimum inventory sizes for each TreM and gives information about the TreM’s life traits, development rhythm, and associated species. This booklet is specifically tailored to boreal and hemiboreal forests.