"Into" (one word) and "in to" (two words) are frequently confused. In what situations should the former be used? The latter?
You should use "into" when it's a question of location, for lack of a better word. "I went into the store," "We went into the field of computer science," "We drank well into the morning," etc..
"In to" just happens sometimes. "I went in to buy some milk." In that sentence the "to" is part of the infinitive "to buy."
If you aren't sure which one to use, change the "in" to "in order" and see if it still works. "I went in order to the store" is wrong, but "I went in order to buy some milk" is good.
source: http://english.stackexchange.com/
