This chapter are dedicated to theory of histopathology of breast. Coloured diagrams and pictures of histopathology of breast are given in detail. A brief write up about contents of chapter is given as introduction in the beginning of the chapter. Normal histology of breast is described initially to provide the basis for better understanding of histopathology. Histopathology of Breast, acute mastitis, subareolar abscess, adenosis of breast, ductal carcinoma, fibroadenoma breast, phyllodes tumor, carcinoma breast, gynecomastia, fat necrosis of breast is described in detail with the help of 20 well illustrated diagrams.