The major task for the petroleum refineries in the very fast developing country like us is to achieve maximum lighter distillates from gradually obtainable heavy and sour crude maintaining the various stringent environment norms from time to time specially for the transport fuels. As such the petrochemicals are literally chemicals from petroleum origin is hidden into the basic objective of the refineries along with the exploration of the heavier stocks from the bottom of the barrel. It also includes the optimum use other equivalent natural sources for eco-friendly products and development of low volume high priced value added products/chemicals. The science of petroleum refining and petrochemical industries are very fluid and there are frequent changes in the technology, policies and demands. In this dynamic stage it is really a difficult task to write book in the developing field for which task has been given to me by constant request from many students in this field throughout our country who happens to read my book on "Advanced Petroleum Refining". I have tried my best to collect information on the petrochemicals and have compiled it for the engineering students with a hope it will also be helpful for faculty members as well research scholars in this field. I have taken help from number of process licencors, academicians and experienced experts in the field for which I am ever grateful to each one of them and acknowledge them individually. I am grateful to the management of Gujarat Refinery, Indian Oil Corporation for giving me permission to publish the book. The Objective of publishing this book is entirely academic and I will be happy for the utilization of it by those interested readers.