Studies of the intermediate-ionization metal-line absorbers provide insights into warm/hot lower-density gas that has been processed through stars in galaxies. These absorbers have been studied primarily using doubly and triply ionized carbon and silicon ions (CIII, CIV, SiIII, and SiIV). CIII arises deep within the spectral range of the Ly α forest and is thus mostly visible at low redshifts where the Ly α forest line density is much smaller. SiIII is adjacent to the Ly α line and is also best surveyed at low redshift. The CIV and SiIV lines are well redward of the Ly α line and thus have visibility over a wide range of redshift. UV and IR spectrographs expanded the redshift coverage from z = 0 to z = 7. 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.