X-ray and UV absorption studies of QSO sightlines provide evidence for hot gas around the Milky Way in the form of highly ionized oxygen (OVI-OVIII). Extended structures of hot gas around galaxies are also suggested by galaxy formation theory and numerical simulations. Due to the challenging nature of the observations, many questions remain open. Where exactly does the gas reside and what are its properties? What is the extent and the total mass of the corona? These questions are important to our understanding of galaxy evolution and are linked to the properties of star formation and stellar feedback processes, structure of dwarf galaxies and IGM gas accretion onto galaxies. We construct unified models for the warm/hot corona which successfully reproduce a wide range of observations (UV, X-ray and other). In our models, the corona is a large-scale structure, extending to the virial radius of the MW, and has a significant gas mass, ~5-10e10 M_sun. We present predictions for absorption and emission observations with future space observatories, such as the ATHENA mission, which will allow to test our models and improve our understanding of the circumgalactic medium.