The term “benign breast diseases (BBDs)” is used to describe a wide variety of mammary clinical entities. They are often referred to as para-physiological conditions in normal breast development. Benign breast diseases are mostly found in young women. In older women, they constitute a differential diagnosis when ruling out a breast malignancy. This chapter deals with the main clinical pictures found within the BBD spectrum. The first section is dedicated to breast development abnormalities from complete agenesis to the presence of supernumerary breasts. Following that is a section on fibrocystic breast changes (FBCs) affecting up to 50% of premenopausal women in the first five decades of life. The following part deals with nonproliferative diseases, followed by the complex family of proliferative diseases without atypia and proliferative diseases with atypia. Benign breast neoplasm and inflammatory benign breast diseases close the line of BBDs. The clinical implications of BBDs are discussed in depth, with particular focus on prescribing oral contraceptives (OCs) and hormone replacement therapy (HRT), by assessing the risk of eventual breast cancer and chemoprevention.