Electromagnetic hypersensitive persons (EHS) attribute their nonspecific health symptoms to environmental electromagnetic fields (EMF) of different sources in or outside their homes. In general, causal attribution is not restricted to specific EMF frequencies but involves a wide range from extremely low frequencies (ELF) up to radio frequencies (RF) including mobile telecommunication microwaves and radar. EHS argue that existing exposure limits were not low enough to account for their increased sensitivities. Results of measurement campaigns are summarized. They demonstrate that environmental fields in the ELF and RF range are usually orders of magnitudes below exposure limits. The rational and biological background of recommended exposure limits are described. The existing scientific studies are reviewed, including investigations on the prevalence of EHS among the general population, ability of EHS to perceive and/or react to exposures to weak EMF (assessed in laboratory provocational studies or to the vicinity of EMF sources studied by epidemiologic approaches), and the existence of a specific symptom cluster, which could characterize a suspected EHS syndrome, or individual EHS-specific factors such as electric perception thresholds, neurophysiologic parameters, and cognitive performance and behavior. However, in spite of the variety of scientific attempts, a causal role of EMF remains yet unproven. This does not mean that the suffering could be ignored. It is recognized that EHS cases deserve help. Therapeutic approaches are described and the conclusion of the World Health Organisation (WHO) is summarized.