Triglycerides, which are the principal ingredients of vegetable oils and algae oils, are chemically converted into biodiesel via catalytic transesteri­fication reaction under mild reaction conditions. The effects of transesteri­fication on selected fuel properties have been examined by Bello, Magaji, and Agge [15]. Their results showed that the density reduces by 7-9%, and the cetane number (CN) increases by 60-78% by transesterification. They also found that transesterification overall tends to make the properties of vegetable oils close to those of petrodiesel [15]. Major parts of ensuing sections of this chapter are devoted to the processing and manufacture of biodiesel and its precursor feedstocks.