The headlights on my car are turning yellow. How can I fix this?

The previous answers all assume that you have "plastic" headlamps. However IF it is your headlamp that is illuminating "yellow" this could be an indicator of a failing alternator. IF it is in fact a yellowing "headlamp cover", see previous answers.

Permatex (I think) makes a kit to refurbish your headlights which will get rid of the yellowing. Ask your local auto parts store.
I prefer to sand mine down and clear coat them however. Here's how I do it:
1. Remove both headlights from the car
2. Wetsand with 1500 grit wetordry sandpaper going in circular motions for about 5 minutes per light
3. Wetsand with 2000 grit wetordry sandpaper in the same technique for the same amount of time.
4. Clean lenses off with a bit of alcohol
5. Spray several coats of clear coat on the lenses with about 10 minutes between coats and let them dry for about an hour when finished.
6. Carefully reinstall the headlights

7. Stand back and admire your like-new headlights. They shouldn't turn back to the yellow since a good clear coat will protect from UV damage.

Yes, you certainly can get rid of them anytime your really want to. You do not need new headlights if you can safely see ahead of you on the road at night and the illumination meets federal requirements for your particular year of car. Of course, this is up to you. It is not likely you will be pulled over and given a citation for yellowing of the headlights.

This yellowing is caused by a reaction of UV light from the sun and a marginal design by plastics engineers when they got the grand idea to formulate the plastics for the headlight. If it really bothers you, go buy a new one, but if not and you can see fine at night, then you will be better off to let it ride.

Most of the answers here are wrong there is a way to restore headlights to thier new appearance and as for a "magic liquid" that can restore in one step, does not exist yet, you can't do with a liquid what someone else can do with good old fashion elbow grease and all American know how! Period! If your in Nrthrn NJ check out www.clearchoicelights.com

That yellow is oxidation. Pittman's Original One Step ALR APC 360ID will remove the oxidation safely and instantly.
It is a pure liquid acrylic lens deoxidizer and conditioner designed specifically to remove headlight oxidation. You won't find it in any auto stores, they only sell abrasive cleaners and sandpaper kits which will ruin the protective UV layer on your headlights and leave them clouded with scratches.
You will have to order Pittman's ALR on line. It is the only product of its kind and it will last the life of your vehicle.

Getting rid of the yellow is more trouble than its worth. best ideas is a total replacement of not one, but both headlights. i have tried everything and total replacement now helps me to see the way.

You can buy this stuff call Plastix at Wal-Mart for like $4.00. It works really well.

Paint them white.

Other than expensive replacements, there are basically four ways you'll find in your search on how to best fix yellow headlights. First, buff with rubbing compound. Second, sandpaper and then buff with rubbing compound. Third, sandpaper and seal with a single component, wipe-on sealer. The trouble with the first two methods is that neither really address the ultimate causes; they just clean the yellow out and temporarily improve clarity. The third method works better, but the quality of these inexpensive sealers can be a gamble and often they may be rated to last a couple years at best. The absolute best way of fixing yellow headlights is to prepare them using sandpaper and a plastic adhesion promoter for application of a two-part, chemically hardened automotive grade clear coat. This is a simple process for most auto body shops or mobile bumper paint repair technicians and will save lots of experimentation, hours of elbow grease, and constant "re-buffing". Automotive clears are rated to last YEARS and have been used to paint plastic for decades. Some may quibble about the type of plastic being different in some cases, but honestly I have never found it to be a problem. Headlights refinished in this fourth way will look brand new. For more information, check out the helpful articles found at http://www.autoworxplus.com