Co-immunoprecipitation, Co-IP in short, is a widely applied technique to identify physiologically-relevant protein-protein interactions by utilizing target protein-specific antibodies to indirectly capture proteins that are bound to this specific target protein. As an extension of IP, Co-IP can capture and purify not only the primary target, but also other macromolecules binding to the target by native interactions. Difference between IP and co-IP is the focus of the experiment. IP is focused on the primary target, which binds the antibody.