I see a lot of confusion about what, exactly, an editor does. That’s because editor is a catch-all word used to describe anyone who helps the author get a manuscript ready for publication. So here is a very simplified way of looking at the different editorial roles you may encounter. Keep in mind, every publishing house and every editor defines their role slightly differently, and there’s a lot of overlap between the levels. If you were to hire an editor for each level, start at the top (developmental editor) and work your way down–proofreading an early draft that will be largely rewritten is a waste of time and money.
This is editing that looks at the story as a whole. The developmental editor will advise on what is or is not working in your story. They’re not going to make many notes in your manuscript, but will give you an overall idea of what to do for your next draft, for example expand dialogue, focus on your character’s emotions, another character is underdeveloped, your action sequences are confusing, etc. The developmental editor will give advice and use examples that are unique to your writing style and story. Rewriting and revising are a huge part of developmental editing.
Content or Line Editor
This editor will look at the story at the paragraph or page level. This is where you may be told to move a section to another part of the story, or be asked to rewrite single scenes rather than an entirely new draft. Line editing is often wrapped into developmental editing or copyediting. It’s also sometimes called content or structural editing.
The copyeditor is looking at the manuscript at the sentence level. I believe this is the level most people are referring to when they talk about editing. The copyeditor cleans up grammar, rearranges sentence structure, tightens up wordiness, etc. This is probably the most critical level of editing to make sure your manuscript has a professional look and feel.
The proofreader is looking at the manuscript at the word, or even individual letter, level. They clean up spelling and punctuation mistakes. Originally, proofreading was completely separate from all other editing, as the proofreader compared the printed proof of a manuscript to the edited draft to make sure all changes were included. With the move to electronic editing, the proofreading role has changed to look more like copyediting at a micro level.