Sphingosine-1-phosphate has emerged as a unique signaling molecule involved in a multitude of pathways and acting both extra- and intracellularly. Therefore, the sphingosine kinases, which produce this lipid mediator, are now in the spotlight: sphingosine kinase activity, once thought to be involved only in intermediary metabolism, now is known to be highly regulated in cells in response to various stimuli as an important component of signal transduction cascades. This review summarizes current information on structure, localization, substrate specificity, activation, and binding partners of sphingosine kinases, and then focuses on recent discoveries on the sphingosine-1-phosphate/sphingosine kinase pathway in relation to mast cells, IL-12 signalling, prostaglandin biosynthesis, and neutrophil priming. Finally, current perspectives on sphingosine kinases as potential pharmacological targets in immune disorders are discussed.