The gonadal hormone 17beta-estradiol is involved in numerous cellular processes. In many cases, 17beta-estradiol actions are imitated by synthetic and natural chemicals in the environment. Their actions differ depending on the target tissue, the receptors involved and the molecular pathways activated. The plethora of estrogenic actions is triggered by different receptors and other specific structures that activate different signalling pathways. This amount of information may lead to a maze of effects triggered by endogenous and environmental estrogens that we intend to clarify in this review. Understanding the variety of estrogen receptors, their different locations and the signalling pathways activated by estrogenic ligands is fundamental for understanding the diversity of actions that estrogens have in different tissues and cells.