Studies on plant metabolism, including those on cereals, increasingly focus on plant phenolic compounds, e.g. phenolic acids and flavonoids. The aim of this study was to present a comprehensive picture of major phenolic acids in grain, starting from their biosynthesis, their occurrence and finally their role in the vegetation of cereals. It is clearly connected with the polygenic plant resistance to pathogens, particularly toxin-forming fungi. Other crucial aspects include the transformations that take place during the technological processing of grain, their metabolic pathway in the human organism as well as the presentation of the health-promoting effect of grain processing products containing phenolic acids. These compounds are used as precursors of bioactive compounds commonly applied both for therapeutic purposes and in the cosmetics, engineering and food industries. An advantage of phenolic acids is the fact that they may be metabolized by microorganisms found in nature and thus they provide an alternative to the increasing load of man-made chemicals in the environment.