The relationship between hormones and the pathogenesis of prostate cancer (PCa) has been studied extensively. All the mainstay targets for hormonal PCa therapies are based on negating androgen action. Recent epidemiologic and experimental data have clearly pinpointed the key roles of estrogens in PCa development and progression. Racial and geographical differences, as well as age-associated changes, in estrogen synthesis and metabolism contribute significantly to the etiology by increasing the ratio of circulating estrogen to androgen, sex hormone binding globulin synthesis, and aromatase activity and reducing androgen glucuronidation and tissue bioactivation. Promotion of aberrant cell growth, evasion of apoptosis, increased oxidative stress and inflammation, and gains in adiposity and bioactivation to genotoxic carcinogens during adulthood are probable mechanisms of estrogen carcinogenicity, while “estrogen imprinting” via epigenetics in early-life also determines PCa risk. Although the effects of estrogens are known to be mediated by genomic actions of the two estrogen receptor (ER) subtypes (ERα and ERβ), other non-canonical mediators, including the different ERβ isoforms, membrane and mitochondrial ERs, and G protein-coupled receptor 30, may have major actions diverging from classical ER actions. These new discoveries have led to renewed interest among the public and the medicinal field in estrogens and antiestrogens as singular and adjuvant PCa treatment and prevention regimens. This review summarizes current knowledge on how different estrogens/antiestrogens/estrogen mimics contribute to prostate carcinogenesis, the roles of the different mediators of estrogen in the process, and the potentials of new estrogenic/antiestrogenic compounds as targeted therapies for prevention and treatment of PCa.