Inherent　twinnability　of　face-centered-cubic　(fcc)　metals　was　analyzed　based　on　the　direct　competition　between　twinning　partial　dislocation　nucleation　and　trailing　partial　dislocation　nucleation,　with　which　the　twinnability　of　fcc　metals　can　be　simply　expressed　as　function　of　the　stacking-fault　energy,　the　unstable　stacking-fault　energy,　and　the　unstable　twinning-fault　energy　of　fcc　metals.　The　predicted　twinnability　ranking　matched　well　with　former　experimental　results　and　provided　a　physical　insight　to　understand　twinnability　from　crystallographic　orientation　and　fault　energy　parameters.