Oxidation of polyunsaturated fatty acids by lipoxygenases leads to a variety of fatty acid metabolites which play important roles in physiology but also in pathophysiology. Data accumulated during the last decade point to the fact that lipoxygenase metabolites are involved in host defence reactions, cardiovascular system and contribute to the development of inflammatory and allergic diseases, cardiovascular disease and cancer. This PIR volume summarizes the physiological and pathophysiological functions of lipoxygenases.