Phenolic acids (PhAs), including hydroxybenzoic and cinnamic asids and their derivatives, are the products of secondary metabolism in plants and play important role in their growth and development. In this book, Chapter One discusses the phenolic acids during growth and development of xylem cells in Pinus sylvestris L. stems. Chapter Two evaluates the possible synergism or antagonism of several phenolic acids allowed to concomitantly react in an antioxidant capacity. Chapter Three evaluates the effect of different solvents on the extraction of major phenolic acids from aerial part of wild and greenhouse cultivated heather. Chapter Four focuses on quantification of the antioxidant activity on five varieties of mole produces in the Huichapan region in Mexico. Chapter Five examines antioxidant and cytotoxic activities of phenolic acids and their role in anticancer therapies. Chapter Six reviews the quantification and characterisation of phenolic acids in foods. Chapter Seven presents an overview on the physiological effects of phenolic acid in tea and coffee on human health.