The paper summarises the exposure limits that have been promulgated by national organisations of different countries, and the rationales that have been advanced for establishing these limits. The limits differ by orders of magnitude, largely because of different philosophical approaches to standard making. The limits were developed, in the first instance, because of concern about high-power radar equipment, but have gradually been extended to cover very much lower frequencies. New standards are being developed in the USA which are much more restrictive as regards RF exposure. The justification for these is examined.