In recent years it has become possible to make electron paramagnetic r
esonance (EPR) measurements at very high magnetic fields. This opens u
p the possibility that there will be an increase in the number of inte
resting cases in which the hyperfine and Zeeman energies in paramagnet
ic species are comparable. With this scenario in mind the role of the
nuclear Zeeman energy in a variety of continuous wave and pulsed singl
e and multiple electron resonance experiments is reviewed.