Phospholipids form a group of phosphorylated lipids that include structures such as a phosphorylated diacylglycerol or ceramide, a nitrogenous base or a polyol (inositol).

Although a satisfactory classižcation of phospholipids is difžcult, we will separate them, as indicated hereafter, according to whether they contain a glycerol or a ceramide. The presence of forms with a direct bond between phosphorus and a carbon atom results in the distinction of one subgroup (phosphonolipids) for each phospholipid group.