Wiring – How to wire a ceiling light with 2 wires to ceiling with 3 wires

What you have is power to the ceiling, and 3-Way switches.

My best guess, is to wire the two blacks together in the ceiling, with a wire nut. One of the whites should be marked. This will go to the Black of the fixture. The other white wire should go to the white of the fixture. And then connect the ground.

So the path will be Panel Hot -> Black wire -> [ Switch Common -> Switch Travellers ->Switch common -> ] WHITE -> Light -> Panel Neutral.

the stuff in Brackets [] is in the wall, and you won't see it.

See this http://diy.blogoverflow.com/2012/01/poles-and-throws/ for more information on 3-way switches.

If the old fixture worked, at least one of the white wires is hot.

The easiest way to check which is hot is to use a non-contact tester. If the fixture is already removed, leave the two wires bundled together with a wire nut over the end. Put a wire nut on the single white wire. Turn the breaker back on. Only one of those should register on tester. That is the hot side. The other should not register. That is the neutral.

Once you know which wire is hot, mark it with black tape or a permanent marker.

If the the fixture is still attached, you can do the same thing with the fixture hanging down. Once you know what is what, turn the breaker back off before wiring.

The black wire goes to the hot wire, the white to the neutral. The ground wire should be attached to a green or bare wire if there is one in the box, or to the box itself if it is metal. If not, just cap it.