INTRODUCTION Immunohistochemistry (IHC) is a powerful method for localizing specific antigens in formalin-fixed, paraffin-embedded (FFPE) tissues based on antigen–antibody interaction (Taylor and Burns, 1974). The technique is widely used in dermatologic diagnostics and research, and its applications continue to be extended because of its ease of use, reliability, and versatility. In IHC an antigen–antibody construct is visualized through light microscopy by means of a color signal. The advantage of IHC over immunofluorescence techniques is the visible morphology of the tissue around the specific antigen by counterstaining, e.g., with hematoxylin (blue). Results of stained IHC markers are reported semiquantitatively and have important diagnostic and prognostic implications, particularly for skin tumors, lymphoma, and the detection of infectious microorganisms. This article presents the key steps for performing IHC and describes its current use in dermatology.