You may end a sentence with a preposition!

It's a common misconception that you should never end a sentence with a preposition. Many grammarians argue that it's perfectly okay to do so, if the case warrants it.

What is a preposition?

A preposition, and the prepositional phrase which contains it, describes a relationship between its object and the rest of the sentence. For example:

The horse is in the stable.
He went inside the house.
The students were very disrespectful toward their teacher.

For a more detailed description of prepositions

When it's okay to end a sentence in a preposition:

Take the following sentence for example:

Who did you talk to?

Try removing the preposition.

Who did you talk?

This doesn't make any sense, and the alternative, rewriting the sentence, sounds too awkward for every day use:

To whom did you talk?

Unless you're writing dialogue for a particularly pretentious character, it would not be a good idea to write this way.

When it's not okay:

On the other hand, if the preposition could be removed without changing the meaning of the sentence, then it should be.

E.g. There was nothing inside of the refrigerator, so they ordered pizza.

There was nothing inside the refrigerator, so they ordered a pizza.

E.g. Where are you going to?

Where are you going?

In each example the second sentence works better, both for brevity and clarity.

Source