Abstract: Exosphere is an essential component of the atmospheres of terrestrial bodies. Its structure and variability hold significant scientific values for understanding planetary material loss, atmospheric evolution, and habitability. This paper systematically reviews the progress in the study of the exospheres of terrestrial bodies over the past 60 years, covering their formation mechanisms, observational and simulation methods, and variabilities. In terms of origin, the exospheres can be classified into three types: lower atmosphere-origin exospheres, surface-origin exospheres, and interior-driven exospheres. After their formations, exospheric particles also undergo various loss processes, keeping the structures of the exospheres in a state of dynamic evolution. Spectroscopic and mass spectrometric measurements are the primary observational methods for studying exospheres, providing essential data for analyzing their structures and variabilities. The classical Chamberlain model remains the most widely used approach for deriving exospheric density distributions. Subsequent developments, including the Boltzmann transport equation and Monte Carlo simulations, further incorporate the effects of particle energization below the exobase, making them particularly advantageous for studying deviations from local thermodynamic equilibrium and the escape of high-energy non-thermal particles. The variabilities of the exospheres are driven by both internal and external factors, including external drivers such as solar cycle, solar flares, physical and dynamical processes in the lower atmosphere, and gravitational interactions in binary systems, as well as internal processes such as geological activities. These factors significantly alter the structural characteristics of the exospheres by affecting the generation and loss of exospheric particles. By reviewing relevant research findings, this paper aims to provide valuable references for further improving the theoretical framework of exosphere formation, elucidating its dynamic properties, and investigating its impact on planetary atmospheric evolution and habitability.