Theoretical concepts in magnetobiology

It is well known that weak, about 1 G and less, magnetic fields (MFs) cause a biological response. Processes of different hierarchic levels of a living organism, from molecular (bio)physical to complex adaptive biological processes, contribute essentially to the effect of MFs on biology. In biophysics, separate magnetosensitive processes at the fundamental level of interaction of fields and substance are studied. It is exactly at this level that complex spectral or ''window'' modes of the relation between biophysical processes and biologically significant MF parameters originate. A review is given of the present situation. The paper concentrates on models that deal with extremely low frequency (ELF) MFs. Theoretical amplitude-frequency limits are considered that constrain possible physical mechanisms underlying biological effects.