By Energetic Neutral Atoms (ENA), we mean atoms having kinetic energies >0.1keV found in and out of the heliosphere. In the regions lacking any neutral gas of temperatures >106K, while abundant in ions of kinetic energies >0.1keV, surely an ENA has to be the product of charge exchange between an ion and an atom or molecule B of the local gas, i.e. A++B → A+B+. Because energy exchange is minute during charge exchange, the newly formed ENA A and ion B+ can be considered keeping their respective original kinetic energies. Instantly, ion B+ is trapped by the local magnetic field, but ENA A is liberated and flies yonder, to be a sample of its originating plasma in mass and energy, thus providing a precious medium for remote sensing the parent plasma. The recent success of NASA's IBEX (Interstellar Boundary EXplorer) Mission in directly detecting ENA coming from the local interstellar medium greatly expanded the scope of ENA remote sensing. Here, we review the discovery of ENA in high altitudes, the basic concept and existing examples of remote sensing of ENA, recent results, and the designs and development of the necessary instruments, and also offer a prospective on ENA-sensing in the near future.