Immunohistochemistry (IHC) has been used to search for specific protein-products, to observe the unique characteristics of breast cancer, to differentiate breast cancer from cancers of other sites origin, to obtain information regarding genetic alterations, to investigate prognostic factors, and to provide predictive factors for efficient treatments. Technical developments make it possible to utilize IHC as a convenient diagnostic tool, and to use it in advanced protocols in combination with other histochemical techniques as well. In this review article, the development of IHC, IHC for differential diagnosis and IHC for providing information about hormone receptors and HER2 in breast cancer practice will be introduced. Standardization and quality control are critical issues to utilize IHC adequately in breast cancer practice.