Simply put, Biodiesel is a direct replacement Diesel fuel derived from Vegetable, Animal and other Organic oils.

Bay far, the most common is derived from Soybeans.  Other plant products can include, canola, corn, sunflower and a host of others.

 The process to create Biodiesel from these oils is called Transesterfication.  It involves changing the molecular structure of the "Fats" in the Feedstock (base oil).  This may sound complicated but its not at all.