In Word, when I hit enter it's "returning" two lines instead of one, even though the line spacing is on 1. How do I change that?

I usually turn all automatic formatting off . I hate it.

Not knowing which version of Word you’re using, I can only point you to the Paragraph Formatting | Line Spacing. You control what happens with the line spacing there (in a couple of ways). Take all values to “0” and be sure that “Single” spacing is selected.

When this happens to me Spacing (in the Paragraph dialog box in the Page Layout tab) is typically the culprit. It is just to the left of “line spacing” and it has two options, the top one says Before and the one just below it says After. Almost always the After spacing is set at 10. It irritates the shit out of me.

This isn’t quite what you’re looking for, but if you hold shift while you press enter, it should do a single line break.

Format / Paragraph / “Spacing after” and “Spacing before”. (Just as @SuperMouse suggested.)

Are you using Styles in the document? You may have a style set up that is different from what you expect, and that’s controlling the layout.

What @digitalimpression, @picante, @SuperMouse & @CWOTUS said is the likely answer. You say it’s generating two lines. Is that so? Can you actually click in the space above where the cursor ends up and start typing there with no extra line space? You could if it wre actually inserting two hard returns. If you can’t, then it’s the paragraph format either before, after or both that needs editing. For a how to on that, consult your help files or post the version of Word you’re using.

And even if there is a paragraph break space turned on, you can use @Mariah‘s trick to get a single linebreak instead of a paragraph break.