Phenolic acids constitute a chemically diverse group of bioactive compounds. The activity of phenolic acids is related to the presence of hydroxycarboxylic groups and their position on the aromatic ring. These are compounds commonly found in nature – they are present in many species of plants and fungi. In the world of higher fungi, they constitute the most numerous group among phenolic compounds. The most common phenolic acids in the world of fungi are caffeic acid, gallic acid, gentisic acid, ferulic acid, p–coumaric acid, p–hydroxybenzoic acid, protocatechuic acid, vanillic acid, and a compound with a structure similar to phenolic acids – t–cinnamic acid. Phenolic acids found in fruiting bodies of mushrooms show, among others, antioxidant, antimicrobial, and anticancer properties.