Book excerpt: This publication details the isolation of proteins from biological materials, techniques for solid-liquid separation, concentration, crystallization, chromatography, scale-up, process monitoring, product formulation, and regulatory and commercial considerations in protein production. The authors discuss the release of protein from a biological host, selectivity in affinity chromatography, precipitation of proteins (both non-specific and specific), extraction for rapid protein isolation, adsorption as an initial step for the capture of proteins, scale-up and commercial production of recombinant proteins, and process monitoring in downstream processing.