The etiology of breast cancer is attributed to a complex interaction between various modifiable and non-modifiable factors. This etiology is determined by genetics, environmental, nutritional, hormonal, and heritable elements that contribute to the development of this disease. Risk factors include prior history of breast cancer, positive family history, obesity, tall stature, smoking, alcohol consumption, early menarche, late menopause, sedentary lifestyle, nulliparity and hormone replacement therapy. Factors associated with decreased risk of breast cancer include multiparity, history of breastfeeding, physical activity, weight loss, and prophylactic surgical and medical Note to the reader: This chapter is part of the book Breast Cancer (ISBN: 978-0-6453320-3-2), scheduled for publication in July 2022. The book is being published by Exon Publications,