Glycerophospholipids are derivatives of sn-glycero-3-phosphoric acid. They contain an O-acyl or O-alkyl or O-alk-1¢-enyl residue at the sn-1 position and an O-acyl residue at the sn-2 position of the glycerol moiety and are defined on the basis of the substituents on the phosphoric acid at the sn-3 position. Glycerophospholipids are asymmetrically distributed between the two bilayers. They not only constitute the backbone of cellular membranes but also provide the membrane with a suitable environment, fluidity and ion permeability. They are synthesized at the endoplasmic reticulum and are transported to other membranous structures by phospholipid exchange and transfer proteins. Once glycerophospholipids are laid down in a biomembrane, they undergo interconversion reactions (base exchange, methylation and decarboxylation). These reactions and activities of phospholipases may be responsible for the turnover, compositional maintenance and rearrangements of glycerophospholipids in membranes. This process results in the modulation of membrane function. Glycerophospholipids are multifunctional molecules. They are precursors for second messengers. In addition, they may be involved in membrane fusion, apoptosis and regulation of the activities of membrane-bound enzymes and ion channels.