Flashbacks, dialog, the "omniscient narrator" -- whatever does the job.
That's why the Michael York guy in the Austin Powers movies is called Basil Exposition. When you have a character telling another character something he already ought to know, that's a good example of bad exposition.
"As you know, 007 --"
"If I already know it, Q, why are you telling me?"
"Because the bloody audience DOESN'T know!"
"Oh, right. Carry on."