We address the subionospheric extremely low‐frequency ( ELF ) radio propagation with an emphasis put on the global and transverse electromagnetic resonance and on geophysical information deduced from resonance parameters. The expected spectra are demonstrated for the global electromagnetic (Schumann resonance, SR ) and the waveforms are given for the ELF transients or Q ‐bursts. Models of ELF propagation constant are presented together with efficient models of the lower ionosphere conductivity that provide realistic SR data in the direct field computations such as FDTD (finite‐difference time‐domain) method. Observational aspects are also addressed, including a brief description of the field sources, instrumentation, and typical signal processing with illustrations of actual data.