Sphingolipids are fundamental to the structures of cell membranes, lipoproteins, and the stratum cornea of the skin. Many complex sphingolipids, as well as simpler sphingoid bases and derivatives, are highly bioactive as extra- and intracellular regulators of growth, differentiation, migration, survival, senescence, and numerous cellular responses to stress. This book reviews exciting new developments in sphingolipid biology/sphingolipidology that challenge our understanding of how multicellular organisms grow, develop, function, age, and die.