Monoclonal antibodies have many applications in biotechnology such as immuno affinity chromatography, immuno diagnostics, immunotherapy, ding targeting, and biosensors among others. For all these applications, homogeneous antibody preparations are needed. Affinity chromatography, which relies on the specific interaction between an immobilized ligand and a particular molecule sought to be purified, is a well-known technique for the purification of proteins from solution. Three different affinity techniques forthe one-step purification of antibodies involving Protein A, thiophilic adsorption, and immobilized metal affinity chromatography (IMAC) are described in this chapter.