This chapter shows that radiators and receptors are somehow different from antennas. It discusses differentiation between radiators, receptors, and antennas is merely to distinguish between structures intentionally designed to radiate and receive. The concept of radiation from, and coupling to, interface cables, printed circuit board tracks, wiring, etc. is generally foreign to engineers, despite involvement with equipment containing digital, analog, radio frequency, and control circuits. The reason may be that it is difficult to envisage interconnections as antennas, or circuit elements, or to see the potential for crosstalk between conductors. Most antenna books are confined to the analysis of antennas that are highly efficient and relatively narrowband. In order to understand electromagnetic waves in proximity to current-carrying conductors as well as in free space, it is helpful to examine static electric and magnetic fields. The distances at which far-field conditions occur are dependent, among other factors, on the size of the antenna.