This monograph is concerned with the health effects of electromagnetic fields in the frequency range of 300 Hz-300 GHz, which includes the radiofrequency (RF) range (100 kHz-300 GHz) covered in the earlier publication (WHO, 1981). For simplicity, RF is the term used in this document for electromagnetic fields of frequency 300 Hz-300 GHz. Within these frequencies are microwaves, having frequencies of between 300 MHz and 300 GHz.