This is the idea that God has determined beforehand who would be saved.  Although no one is worthy of salvation, God chose in eternity past who would be saved.

Some reach the natural conclusion that if God predestines some for heaven, God predestinates the rest to hell.  This is referred to as double predestination. 

Others simply say that all are destined for hell but God in His grace chose some for salvation and that by not choosing others, He does not condemn them to hell because they were already destined for it.

The question must be asked why God would choose to save some but not others if He desires all to be saved and is capable of saving all.  Supporters claim that God is glorified even in sending people to hell, much as a diamond looks more dazzling when set against a dark background.

See also: Unconditional election