This atlas illustrates the range of breast lesions with detailed correlation of gross and microscopic features. Where relevant, radiological images are incorporated.  A description of normal, developmental and physiological breast morphology will serve as introduction to the main content of this atlas. Classification of tumors is based on the latest World Health Organization Classification of Tumors of the Breast, 4th edition, 2012. As immunohistochemistry is a key adjunctive tool in the workup of breast lesions as well as used in prognostic evaluation of breast cancers, appropriate examples are interspersed among the lesions where pertinent.