• Radio synchrotron and hard X-ray bremsstrahlung come from the same electrons: can compare them quantitatively
• Nonthermal electrons emit radio waves very easily: can see the morphology of the emitting source in radio images
• Radio polarization tells up something about the magnetic field geometry
• Correlating light curves of different sources provides strong constraints on magnetic connections
• Can also see coronal density via free-free emission prior to flares (1011 cm-3 densities are optically thick at coronal temperatures and would produce very strong radio emission)