What are the different generations of biofuels?

Biofuels are classified by feedstock and production technology: First generation - made from food crops like corn, sugarcane, and vegetable oils; includes ethanol from sugar/starch fermentation and biodiesel from transesterification of oils; raises food vs fuel concerns. Second generation - made from non-food biomass like agricultural residues, wood, and dedicated energy crops; requires pretreatment to break down lignocellulose; addresses food competition but more complex processing. Third generation - derived from algae; high productivity, doesn't compete with food/land; still developing economically viable scale-up. Fourth generation - engineered organisms (synthetic biology) designed for direct fuel production; carbon capture concepts. Each generation aims to improve sustainability, reduce competition with food, and increase efficiency.