Estrogens are compounds that have a wide range of activities in the human body. These hormones regulate processes, such as the ovarian cycle, sexual development, preparation for implantation of fertilized embryos, and others. The most abundant estrogen in humans is estradiol. It exerts its effects through an estrogen receptor that functions as a transcriptional factor. The mechanism of action of estrogens involves the recruitment of co-regulator proteins that allow, or not, classical transcriptional activity and the transcriptional activation or repression of target genes. Non-genomic actions of estrogens have been reported, and these effects are mediated by a G-coupled protein receptor. Estrogens not only participate in physiological processes, they are also involved in pathology, such as cancer. Breast cancer is one of the main cancers that is affected by estrogens, as there is a higher expression of estrogen receptor α in breast cancer than in normal breast tissue. In this way, estrogens also participate in the development of other cancers including colon, ovarian and cervical cancer. Pharmacological strategies for estrogen related cancer treatments have been developed. Selective Estrogen Receptor Modulators (SERMs) and Aromatase Inhibitors (AIs) have been developed to antagonize the effects of estrogens, or estrogen synthesis, respectively. The use of tamoxifen and other compounds are effective in the treatment of some cancers, including breast cancer. Furthermore, change in lifestyle choices to help reduce xenoestrogen exposure is also a step that a woman can take to control total estrogen exposure.