The first step in purification of an important class of therapeutic proteins, the polyclonal or monoclonal antibodies (mAbs), is their capture from plasma or tissue culture supernatants. Protein A–based media are by far the most common class of affinity products used for this purpose. They bind with high affinity to the Fc region of most subclasses of antibodies and are one of the standard tools used in antibody capture and purification. In combination with ion exchange and ceramic hydroxyapatite chromatography, protein A–based resins have been successfully used in the large-scale purification of numerous licensed mAb drugs.