An octafluoride is a compound or ion with the formula [M_mR_nF₈]^q− or [M_mR_nF₈]^q+, where n, m and q are independent variables and R any substituent and M is a central element (often a metal). All of the examples listed below are [MF₈]^q− with q between 1 and 4 inclusive.

No electrically neutral octafluorides are currently known to exist, although osmium octafluoride, OsF₈, is theoretically possible. An early report of the synthesis of OsF₈ was much later shown to be a mistaken identification of OsF₆.^[1]

In contrast, many anionic octafluorides are known, such as the octafluorozirconate(IV) ([ZrF₈]⁴⁻), octafluorotantalate(V) ([TaF₈]³⁻), octafluoroniobate(V) ([NbF₈]³⁻),^[1] octafluoromolybdate(VI) ([MoF₈]²⁻),^[1] octafluorotungstate(VI) ([WF₈]²⁻),^[1] octafluororhenate(VII) ([ReF₈]⁻),^[1] octafluoroiodate(VII) ([IF₈]⁻), octafluoroiridate(VII) ([IrF₈]⁻),^[2] and octafluoroxenate(VI) ([XeF₈]²⁻) anions.