A variety of high-pressure and low-pressure plug flow reactors (PFRs) are described in this chapter with manufacturing examples for each. Coiled tube PFRs and vertical pipes-in-series PFRs were used for two-phase gas–liquid reactions. A pulsating flow coiled tube PFR was used for gas–liquid reaction with solids precipitate. Superheated PFRs were used for reactions involving homogeneous solutions, heated above the boiling point of the solvent. Disposable coiled tube PFRs were used with highly potent compounds. Continuous stirred tank reactors (CSTRs) were needed for heterogeneous continuous processes. CSTRs, CSTRs-in-series, and intermittent flow CSTRs were used for reactions with long reaction times, positive order kinetics, and multiple reaction phases, either solid/liquid or liquid/liquid. This chapter also explains how to calculate the actual internal temperature profile along the length of a PFR, which is often not practical to measure.