An endocrine disruptor compound (EDC) is “an exogenous substance or mixture that alters function(s) of the endocrine system and consequently causes adverse health effects in an intact organism, its progeny, or (sub)populations (WHO, 2002).” Since the endocrine system consists of a set of biological communication pathways between different organs and tissues, endocrine disruption is the first example of a toxic mechanism altering biological communication. The most studied EDCs target the sex steroid and thyroid systems. Several key characteristics of EDCs have been defined and most of them involve biological communication (e.g. receptor interaction, signal transduction of hormone metabolism). Studies on the human and animal impacts of EDCs have focused on reproductive toxicity, metabolism disruption, mental effects and cancer, but other outcomes have also been described. Long term effects have been studied, in particular when exposure to these substances occurs during the critical early life vulnerable periods. The characterization of endocrine disruptors has triggered an update of concepts in toxicology, e.g. low dose effects, non-monotonous dose-response curves, effects of mixtures, which is relevant for all toxicity pathways involving the disruption of biological communication.