Macromolecular reaction engineering is concerned with polymer production. It provides the critical bridge between bench-scale chemistry and full-scale commercial production. It covers a wide range of subjects from kinetics, to reactor design, to process optimization and control, to safety and environmental impact. In polymer production, we must study three areas: mechanism (condensation, radical, ionic, Ziegler–Natta, etc.), process (bulk, solution, suspension, emulsion, slurry, gas-phase, etc.), and reactor system (stirred tank, tubular, fluidized-bed; batch, semibatch, continuous, etc.). This chapter intends to introduce some basic concepts and recent advances with an emphasis on equation-based quantitative analysis and discussion.