Studies of the high-ionization metal-line absorbers provide insights into hot diffuse gas that has been processed through stars in galaxies. In the ultraviolet and optical bands, these absorbers have been studied primarily using five-times ionized oxygen (OVI), six-times ionized nitrogen (NV), and seven-times ionized neon (NeVIII). Both OVI and NeVIII arise within the spectral range of the Ly α forest and are thus mostly visible at low redshifts where the Ly α forest line density is much smaller. NV is adjacent to the Ly α line and in principle can be surveyed over the full range of redshift; however, this ion is found in only a narrow range of astrophysical conditions. The population statistics measured include the redshift path density, the equivalent width and column density distributions, the cosmic mass densities, and the kinematics (broadening parameters, velocity splitting distributions, and absorber velocity widths). In this chapter, we discuss multiple observational programs and their reported findings for several of these ions.