Publisher Summary Though other isomers occur naturally, the myo form of inositol (I) is most widely distributed in living tissues. It has been found in tapeworms, whales, land mammals, fruit flies, fish, spinach, bacteria, tobacco plants, yeasts, algae, and arid acorns. One important aspect of inositol function lies in the provision of these lipids that are almost as widely distributed as inositol itself. This chapter discusses the chemical structures, biosynthesis, and catabolism. The chapter focuses on the assessment of the possible relation between inositide metabolism and cation transport. It summarizes the present knowledge of the distribution of phosphoinositides among living organisms. A closer study of the relation between nervous activity arid the metabolism of the inositol lipids should be rewarding. In view of the widespread interest in mitochondrial function, particularly oxidative phosphorylation, there is no doubt that, studies of these lipids in mitochondria will be actively pursued.