The first committed step in TAG synthesis via the glycerol phosphate pathway is the acylation of glycerol 3-phosphate by glycerol-3-phosphate acyltransferase (GPAT) enzymes, which reside in the endoplasmic reticulum (ER) and mitochondria (reviewed in Refs. 40 and 43). An additional fatty acid is subsequently transferred to lysophosphatidic acid (LPA) by the family of 1-acylglycerol-3-phosphate acyltransferase (AGPAT; also known as LPA acyltransferase) enzymes to produce phosphatidate (reviewed in Refs. 3 and 106). Phosphatidate occupies a branch point in lipid synthesis. It can serve as a precursor of acidic phospholipids or of diacylglycerol (DAG). The conversion of phosphatidate occurs through the action of phosphatidate phosphatase-1 (PAP) enzymatic activity, which is conferred by the lipin family of proteins (reviewed in Refs. 99, 100, and 102). Finally, the resulting DAG is converted to TAG through the action of diacylglycerol acyltransferase (DGAT) enzymes or used in phospholipid synthesis via the Kennedy pathway (reviewed in Refs. 114 and 129). The resulting TAG is used in several metabolic processes, including synthesis of very-low-density lipoproteins in the liver and chylomicrons in the intestine, energy storage as lipid droplets in adipocytes, and milk production in mammary epithelial cells. TAG can also serve as a sink for potentially toxic fatty acids and acyl-CoAs within cells.