The Fluid Catalytic Cracking Unit (FCCU) is a major unit in modern refinery which converts heavy petroleum fractions using special catalyst into more usable products such as gasoline, middle distillate and light olefins. The FCCU consists of the reactor (riser reactor, reactor catalyst stripper, reactor separator or disengager, reactor cyclones, etc.), the regenerator and the main fractionator. Many evolutionary changes in the FCCU have occurred since 1942 and over these years the configuration of the FCCU, the catalysts and FCC hardware had been considerably improved. The kinetic lumping schemes have also increased. This study should help to shed more light on the advances in the FCCU and should be useful to all who directly or indirectly use gasoline (Petrol) and other similar products.