Fungi are the principal decomposers of wood together with xylophage insects and, as such, have a central role in nutrient cycling of forest ecosystems. These fungi are also envisaged as promising tools for converting wood and waste of wood industries into chemicals, as alternative to fossil chemicals. At the same time, wood decomposers pose a threat to wooden building materials and are intensively fought. As a consequence, intense researches have been conducted over the past 50 years to identify the fungi responsible for wood decomposition, the mechanisms by which they do so, the wood properties involved in resistance or sensitivity to attacks and ways to preserve woods. Many tools are now available to study fungal colonization of wood, including: "omics" techniques, enzymatic assays, spectrometry, etc. However, all these approaches provide bulk information and the data obtained by these methods contain no information on the localization of fungi, the stage of decomposition of the wood and the potential interactions between microorganisms. In these regards, microscopy approaches provide complementary information that can strengthen conclusions. The present chapter describes a diverse range of microscopy approaches, from simple bench light microscopy to confocal and electron microscopies, to shed light on the way fungi colonize wood tissues.