This chapter synthesizes the electrical and dielectric properties of some biological functional and structural units, such as cells and various tissues of different organs, and analyzes their interaction with the earth’s natural electric field and with artificial electromagnetic fields (EMFs) of low and high frequency, mentioning some biological and health effects reported in the scientific literature. The case of passive metal implants and prostheses used to replace structures or support tissues which act as antennas that more efficiently capture radiofrequency EMFs (by resonance effects) as those that characterize current wireless communications systems that induce EMFs and currents of the same frequency as incident waves that alter the electromagnetic ecosystem of tissues and organs, is also analyzed.