Flare stars appear to be as common among the hottest stars as among the coolest. Starspots, which are closely associated with flares, are likewise common among stars of all spectral types. This finding contradicts the long-help belief that only stars with convective envelopes can sustain magnetic fields. It is found that rotation is a dominant factor in inducing flares: flare stars nearly always have shorter rotation periods than non-flare stars. These findings have important implications for the atmospheres of A and B stars as well as providing clues for the formation of the corona.