Caffeic acid is one of the hydroxycinnamic acids, a subgroup of natural phenolic acids. It is synthesized by plants as a secondary metabolite and it naturally occurs in the form of derivatives, such as glycosides, amides, and esters. The largest and best-characterized group of caffeic acid derivatives are its esters formed with chinic (chlorogenic), α-hydroxydihydrocaffeic (rosmarinic), and tartaric (caffeoyltartaric) acids as well as caffeic acid phenethyl ester (CAPE). Those compounds are present in a variety of fruits and vegetables, thus, they are natural components of the diet. Caffeic acid, its natural derivatives, and synthetic analogues are potent antioxidants, which, even in low concentrations, protect cells from oxidative stress. It was proved in many experimental systems that the caffeic acid and its derivatives effectively scavenge reactive oxygen species (ROS), chelate metal ions, and have an inhibiting effect on lipid peroxidation. CAPE deserves particular attention since it shows the strongest antioxidant activity.