Anti-Ballistic Missile defence system of somekind, possibly using advanced lasers in the future or smaller missiles capable of intercepting ICBMs. Entirely theoretical, currently impossible due to Multiple Independant Re-Entry Vehicle technology, i.e., warheads "open" and launch over a dozen smaller warheads at targets hundreds of miles apart; maybe lasers will be powerful enough one day or we'll find some way of intercepting missiles before they launch multiple warheads.

MIRVs are quite terrifying, one missile could wipe out half of a nation. Or in case of Finland, the whole nation and then some

I usually think of something like this: http://t0.gstatic.com/images?q=tbn:ANd9GcQrCDTx8ogDHCZFDU4sor5IeWot7ABUuCwlOkmy-yAlLShUFSUTvw

This. Definitely this. I WANT FRIGGEN LASERS ON MY FRIGGEN SATELLITES!

Well, without thinking about it, I interpreted "missile shield" like a medieval style tower shield...that just happens to be really good at protecting people from missiles.

After actually thinking about it, I'm going to guess that a missile shield is some kind of radiowave-type of thing that disables incoming missiles within a certain radius.

I assume a missile shield would be the same as having these "anti missile" thingies shooting down incoming missiles with other missiles or something.

Like a kite shield, only it explodes and deals fire damage when you bash with it.

Maybe I've been playing too much Skyrim.

Perhaps something like this: http://www.youtube.com/watch?v=k2ymFv1gKZ8 ?

I, too, am thinking it's what the OP thought. Missiles shot at incoming missiles.

The US Navy is developing/experimenting with rail guns. They've still got a long way to go, but they have built functional models.

What is with The Japanese and non functioning angel/demon wings?

Them carbon dioxide lasers or copper vapor on 757s and nuclear nikes from space

A point-defence system that includes computer-targeted CIWS, anti-missile missile batteries, and electronic warfare and/or other diversionary countermeasures. Most commonly deployed to protect a fleet, particularly carrier flotillas that are vulnerable to standoff anti-ship missile attacks.

This, more or less.

I've always imagined a missile shield as a series of enormous pigeon coops placed around the edge of a country. When incoming missile are detected, the pigeons are released. The enormous cloud of birds then fly up and block the missile, ensuring safety, security and roast pigeon for all.