An octafluoride is a compound or ion with the formula [MmRnF8]q- or [MmRnF8]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.

Neutral octafluorides

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.

Anionic octafluorides

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