Coimmunoprecipitation or CoIP is a type of immunoprecipitation technique that is used to study protein-protein interactions in vivo. It is based on the potential of IP reactions to capture and purify the primary target (i.e., the antigen) as well as other macromolecules bound to the target by native interactions in the sample solution. Protein components are visualized by Western blotting using antibodies specific to the different components.