Certain bacteria degrade wood by creating tunnels in cell walls. Transmission electron microscopy (TEM) has played a key role in understanding the intricate architecture of the tunnels produced within the cell wall and the process of cell wall degradation. The most prominent feature of tunnels is the presence of periodic crescent-shaped slime bands, which is the single most important diagnostic characteristic of bacterial tunneling-type cell wall degradation. The review presented covers the aspects relevant to understanding bacterial tunneling of wood cell walls, emphasizing the importance of the application of TEM in this area of research.