The manufacturing processes for polystyrene (PS) and its copolymers, including styrene-acrylonitrile (SAN), high impact polystyrene (HIPS), acrylonitrile-butadiene-styrene (ABS), styrene-butadiene latex (SBR for coatings), styrene-butadiene block copolymers (SBS), and styrene-acrylate copolymers (SMMA), are discussed and illustrated. The synthetic methods for such products are bulk, emulsion, suspension, and free radical polymerization techniques, all either in batch or in continuous operations. By comparison, it was found that continuous bulk is the most economical process among the above-mentioned polymerization methods. However, the suspension method is still the only way to make expandable polystyrene beads (EPS).