The tough, hoof-shaped fruiting bodies of the tinder conk mushroom, Fomes fomentarius (L.) Fr. (Polyporaceae, Agaricomycetes), were traditionally used all over the world as tinder to start fire, for ritual purposes, to make artworks like clothing, frames, ornaments, and also to cure various human diseases (wounds, gastro-intestinal disorders, liver-related problems, inflammations, various cancers, etc.). The first wave of scientific interest in F. fomentarius in Europe dates back to the early 1970s with the discovery of the red-brown pigments of the F. fomentarius external layer. Since then, a number of research papers and reviews have mentioned the history of use, taxonomy, composition and medicinal properties of some F. fomentarius preparations, e.g., soluble extracts and their fractions, isolated cell walls, mycelia and compounds purified from the culture broth. The present review is focused on the composition and benefits of the water-insoluble cell walls obtained from the F. fomentarius fruiting bodies. Isolated cell walls of the tinder mushroom reveal a fibrous hollow structure with an average diameter of 3-5 μm and a wall thickness of 0.2-1.5 μm. Naturally, the fibers are composed of 25-38% glucans, with a majority of β-glucans, around 30% polyphenols, 6% chitin and less than 2% hemicellulose. The percentage of the main structural compounds can vary either slightly or considerably, depending on the extraction conditions. According to in vitro, in vivo, ex vivo as well as clinical studies, F. fomentarius fibers can modulate the immune system, contribute to intestinal health, accelerate wound healing, absorb heavy metals, organic dyes and radionuclides, normalize kidney and liver function, and provide antibacterial, antiviral, antifungal, anxiolytic, anti-inflammatory and analgesic effects. Multiple action of the insoluble cell walls purified from the F. fomentarius fruiting bodies is particularly effective in the treatment of chronic, recurring, complicated multifactorial diseases. It is certainly worth exploring the medicinal potential and the practical application of these preparations further.