This chapter focuses on the final available issue date considering that the latest revised version covers the most updated technologies relevant to the development. In the 1940s, the fluid catalytic cracking (FCC) units were taller with dense bed reactors made of carbon steel. Major developments in the FCC technology took place after the invention of using zeolites at higher activity when compared to former catalysts made of amorphous alumina in the 1960s. FCC feed, namely gas oil, is mainly a blend obtained from refinery units such as crude, vacuum, solvent deasphalting, and coker. Hydrocarbon types in the FCC feed are mainly paraffins, olefins, naphthenes, and aromatics. FCC additives are also used for reduction of the pollutant gases. In the FCC units, thermal cracking via free radicals is minimized mainly by process modifications in feed, riser sections, and proper catalyst selections.