Immunohistochemistry (IHC) is a method for detecting specific antigens in tissue sections or cells using antibodies. Direct IHC uses a primary antibody conjugated to a fluorophore for visualization of antigen expression. Due to limited sensitivity of direct detection, indirect antigen detection methods employing secondary antibodies and other amplification techniques are often preferred. These methods include enzymatic amplification, avidin–biotin complex formation, catalyzed analyte reporter deposition, and rolling circle amplification. The development of antigen retrieval techniques and diverse, photostable fluorophores has further increased the utility and multiple antigen detection capabilities of IHC. IHC has become a powerful tool for addressing both basic hypotheses in experimental pathology and diagnostic issues in the clinical practice of pathology.