Different natural products from the plant kingdom including isoflavones, prenylflavones, cournestans, stilbenes, and lignans can cause endocrine perturbations, especially on the estrogenic hormonal pathway because of their structural analogies to estradiol. Several studies report the presence of such compounds in food, the richest source being soy and soy products These substances, commonly called phytoestrogens, are known to influence the human hormonal profile and soy preparations are being considered for use as post-menopausal estrogen replacement therapy. Numerous clinical and epidemiological reports have studied the influence of phytoestrogens on the development of hormone-dependent cancers. The effect on genital development of postnatal phytoestrogen exposure is still under debate. Consumption of phytoestrogens may also influence the incidence of bone diseases, atherosclerosis, or Alzheimer's disease. This article summarizes the classification of phytoestrogens, their pharmacological evaluation and properties, and the methods used for their identification.