Phenolic acids are secondary plant metabolites belonging to polyphenol classes, widely spread throughout the plant kingdom. The name "phenolic acids", in general, describes phenols that possess one carboxylic acid functionality and they could be divided into three major subclasses: hydroxybenzoic, hydroxycinnamic and hydroxyphenylacetic acids. The great interest in phenolic acids is associated with their high potential for food preservation (antioxidant and antimicrobial activity) and, last but not least, high therapeutic potential. The aim of this review is to summarise the current knowledge concerning phenolic acids and the topics discussed include natural sources of phenolic acids, biosynthesis and metabolism, health benefits of phenolic acids (first of all the antioxidant activity of dietary phenolics and also anticarcinogenic and anti-inflammatory effect), their antimicrobial activity for selected groups of bacteria and fungi (yeasts) and structural modifications of the molecule especially those increasing lipophilicity and improving solubility in lipids. Recent advances in the methods of enzymatic synthesis of phenolic acid derivatives are described and some conclusions referring to Structure-Property-Activity Relationships of phenolic acids, particularly important from the point of view of their pharmaceutical and nutritional applications, are discussed.