Breast cancer continues to be worldwide public health concern in America and Western Europe as the commonest cancer among women and the second highest reason of cancer death. Epidemiological evidences implicating environmental and lifestyle risk factors in breast cancer etiology are accumulating. In this review, the current state of knowledge is reviewed, pertaining to relationship between environmental exposures (persistent chemicals, radiation, electromagnetic fields), lifestyle (physical activity, diet, obesity, smoking, alcohol use, oral contraceptive, hormone replacement therapy) and breast cancer risk. This paper also summarises the epidemiological literature on the cellular mechanisms of steroidal estrogens metabolism to carcinogenic products. The epidemiological data have shown that investigation of breast cancer risk among women is difficult to study because of confounding or modification from reproductive female characteristics. Moreover, multiple factors, known as well as unknown, may contribute to the breast cancer development. Through the inconsistencies and contradictions that appear to exist in the literature with respect to the role of environmental and lifestyle factors in genesis of breast cancer, several factors have been identified that are likely to have a major effect on breast cancer risk. Radiation exposure has been a well-defined environmental factor for breast cancer, especially at young ages. The environmental hazard chemicals and electromagnetic fields exposition are discussed as potential mammary carcinogens, but association between those environmental causes and breast cancer risk was not confirmed. Obesity in postmenopausal women and sedentary lifestyle increase the risk of breast cancer. Moderate to high levels of the alcohol consumption, current oral contraceptive use, especially by young women, and prolonged use of hormone replacement therapy causes a moderate increase in the risk of breast cancer.