How can I remove screws with stripped heads?

I have wood screws whose heads are stripped from trying to remove them with a drill. The drill (or screwdrivers) can't grip the heads anymore. What can i use to remove these screws easily?
Question from user LordHits at stackexchange
Answer:
Damaged screws are extracted by drilling into the screw with a drill bit, then using a special screw extractor bit that is tapered and has threads which turn opposite to those of the screw.
The extraction process should be done slowly and carefully because the extraction process is more fragile than the normal insertion of a screw.
Answer from user Jeff Ferland at stackexchange

I have wood screws whose heads are stripped from trying to remove them with a drill. The drill (or screwdrivers) can't grip the heads anymore. What can i use to remove these screws easily?
Question from user LordHits at stackexchange
Answer:
Damaged screws are extracted by drilling into the screw with a drill bit, then using a special screw extractor bit that is tapered and has threads which turn opposite to those of the screw.
The extraction process should be done slowly and carefully because the extraction process is more fragile than the normal insertion of a screw.
Answer from user Jeff Ferland at stackexchange

