Modern radio-optical methods in quantum magnetometry

This paper is an extension of a part of the talk delivered under the more general title "Narrow spectral lines in fundamental metrology: state of the art, prospects, and problems" at the session of the 90th anniversary of Physics-Uspekhi. The talk reviewed past developments and the current status of the metrology of length, frequency/time, and magnetic fields. The measurement of these quantities currently relies on the high stability of energies of standard transitions between metastable atomic states. Because of space restrictions in the journal, all metrology topics other than the title one were omitted in the present review.