Attention is focused here on the quasilinear and nonlinear physics of cyclotron interactions between magnetospheric whistler mode waves and energetic electrons on dipolar geomagnetic ux tubes. These interactions can lead to the generation of noise-like emissions or phase-coherent discrete signals in the frequency-time domain. In the magnetosphere noise-like emissions called hiss are accompanied by a smooth electron precipitation pattern. Examples of discrete emissions are ELF=VLF chorus or VLF emissions triggered by whistlers from lightning or by radio transmitters on the ground. The rapid temporal variations of these signals are associated with ÿne structure of the distribution function of the radiation belt electrons, such as a transient step-like deformation or a well-organized beam, which are prepared by initial noise-like emissions or by a quasimonochromatic whistler-wave packet, respectively. These cause the properties of the electrons, which may be observed on a satellite, to evolve rapidly in time and on relatively short spatial scales. Bursts of precipitating electrons occur, and can contribute signiÿcantly to depleting the radiation belts. Recent results on improvements in the theoretical understanding of such processes and on new observations of magnetospheric electrons and whistler-mode waves are presented.