The oxygenation of arachidonic acid and other polyunsaturated fatty acids by a wide variety of cell types results in the formation of several structurally distinct classes of biologically active compounds. These compounds include the prostaglandins, thromboxanes, leukotrienes, and other oxygenated derivatives of polyunsaturated fatty acids. A most recent addition to this family of biologically active compounds is the lipoxins (Figure 1). Leukotrienes and lipoxins are formed by mechanisms which involve initial oxygenation of free fatty acids by lipoxygenases. In general, lipoxygenase products display a wide range of actions and appear to be involved in immunity, the regulation of inflammation, and other physiological and pathophysiological processes. In this chapter we describe results of recent studies on the isolation, biosynthesis, stereochemistry and biological activities of this new series of compounds (lipoxins).