The following links are pages that provide helpful information about editing.
This page from the Science Fiction & Fantasy Writers of America site discusses why writers need editors and what writers should look for in an editor.
An author posts about “Why You Need a Professional Editor.”
Sometimes a project quote from an editor seems like a huge amount, and for indie authors who are paying out of pocket it truly can be expensive. But here’s a blogger who understands and explains why editing costs so much: Why Are Book Editors So Expensive?? and The Other Reason Book Editors Are SO Expensive
After reading the above two posts explaining why editing is expensive, here’s a good follow-up post to read about the value of editing and why an author should make the investment: What Is the Value of an Editor?
10 Things Your Freelance Editor Might Not Tell You–But Should: The first section of this page has a good description of the various types of editing that are available. The rest of the page has some great information to consider when working with an editor.
“Do I Need a Proofreader, an Editor, or Both?” — a helpful article that describes the different levels of editing.
Another helpful article: “4 Levels of Editing Explained: Which Service Does Your Book Need.”
This blog post about “How to Brief Your Editor” has some good explanations and even includes a handy document at the end with a list of exactly what information would be helpful to your editor to make the project run more smoothly.