Summarizing the content of this book, we conclude that whistler and Alfvén mode cyclotron masers in space parallel the family of ground-based maser systems in the laboratory, ranging from optical quantum generators to gyrotrons and free-electron lasers. They all require an active medium and a spatial geometry with mirrors at both ends. Many features of whistler and Alfvén maser operations reveal similarities to the operation of optical quantum generators; these include relaxation oscillations, self-oscillation generation regimes, and passive and active mode synchronization. Such regimes occur in cyclotron masers when the energetic electrons have a broad velocity distribution (i.e. the electron velocity range, or dispersion, is similar to the mean electron velocity).

CMs operating in the Earth's magnetosphere explain quantitatively features of many phenomena observed in the ELF/VLF frequency range, such as whistler-mode hiss and quasi-periodic emissions bouncing between conjugate hemispheres; they also determine the dynamics of electrons in the van Allen radiation belts and of pulsating auroral patches. Similar regimes operate for the proton CM and Alfvén waves, but with changes to the frequencies and characteristic time scales corresponding to the proton to electron mass ratio of 1836. Thus cyclotron masers control both the spatial and temporal distributions of the energetic charged particle populations, the Earth's radiation belts, trapped in the dipolar geomagnetic field. These have practical consequences, one example being to specify the radiation dose suffered by instruments aboard satellites in a circular low Earth orbit, in an elliptical orbit or in geostationary orbit.