Immunohistochemistry or IHC refers to the process of detectingantigens in cells of a tissue section by exploiting the principle ofantibodies binding specifically to antigens in biological tissues. IHC takes its name from the roots "immuno" in reference to antibodies used in the procedure, and "histo," meaning tissue.

Immunohistochemical staining is widely used in basic research to understand the distribution and localization of biomarkers and differentially expressed proteins in different parts of a biological tissue.

Visualising an antibody-antigen interaction can be accomplished in a number of ways. In the most common instance, an antibody is conjugated to an enzyme, such as peroxidase, that can catalyse a colour-producing reaction. Alternatively, the antibody can also be tagged to a fluorophore, such as fluorescein or rhodamine. There are direct and indirect immunohistochemical methods for detecting antigens in a tissue section.

The direct method  isaone-step staining  method and involves a labeled antibody reacting directly with the antigen in tissue sections. The indirect method involves an unlabeled primary antibody that binds to the target antigen in the tissue and a labeled secondary antibody that reacts with the primary antibody.