Immunocytochemistry (ICC) is a valuable set of methodologies routinely used in basic and applied biological research and for diagnostic purposes in the pathology laboratory. The various ICC labeling procedures can be classified according to the detection system employed (i.e., fluorescence, chromogenic, or particulate) and whether labeling occurs before or after embedding the sample. ICC localization can be achieved at both the light microscopy (LM) and electron microscopy (EM) levels. Detection of cell or tissue antigens, by means of ICC, relies upon the specificity of the antigen-antibody interaction.