Fetal Bovine Serum (FBS) is a complex mixture with low and high molecular weight biomolecules exhibiting optimal growth-enhancing and growth-suppressing functions. FBS contains molecules such as growth factors proteins vitamins trace elements hormones etc. These molecules are important for the growth and maintenance of cells. It is a common supplement for cell culture media. FBS is derived from the calf blood. It is devoid of fibrin and clotting factors. Heat inactivation of FBS blocks the complement system. FBS derived from clotted blood is the most widely used undefined supplement in eukaryotic especially mammalian cell culture. It is typically used with the classical media that were developed in the 1950s and 1960s. These include many popular media such as Minimum Essential Medium (MEM) Dulbecco Modified Eagles Media (DME DMEM) Iscove Modified Eagles Medium (IMDM) M199 and Roswell Park Memorial Institute medium RPMI-1640.