This chapter reviews the basic equipment and methods applied to processability testing of polymers. It provides an overview of techniques aimed at relating rheological characteristics observed from laboratory studies to commercial processing of polymers. The use and interpretation of rheological flow curves are heavily relied upon to understand and project the processing characteristics of polymers and other non-Newtonian materials. The transition region is usually quite distinct for monodispersed polymeric melts, and broad for polydisperse melts. In the case of SBR mixing, the polymer Mooney viscosity test results were found to have a high degree of correlation with the early mix energy, as did Monsanto Processability Tester shear stress values. Narrow-molecular weight distribution polymers tend to demonstrate higher throughput rates in extrusions, with extrudates typically having smooth surfaces. In rubber applications, dies are usually cut to accommodate the article’s tolerances based on the characteristics of a single polymer supply or fixed blend production.