Will my charger work overseas

All genuine Apple charging bricks support input from 100 to 240 VAC and 50 to 60 Hz. So yes, that covers the planet. Only thing you will need is how to plug the thing into whatever kind of outlet your destination might have. Either buy a cheap US/NEMA to whatever adapter at an electronics store (or airport goodie shop), or invest in Apple's Travel Kit that has all the adapters you might possibly need.

Copy/paste this link on another browser window in case the inlined link above does not work: http://www.apple.com/us/search/Travel+Adapter+Kit?src=globalnav

This shows an Apple charger with the power plug removed and an extension cord plugged in. You can either get a plug that matches the wall outlets where you will be going or get an extension plug to plug into the charger with the other end matching your country.

In that case, you will need an adapter from the regular US 2 or 3 prong plug to what they have there. Maybe a bit unsightly and cumbersome, but better than having to buy another brick. Or follow Illass' suggestion, once you remove the 'duck's bill' adapter from the brick.