I have seen both Art Director and Creative Director as titles, but I'm not sure what the difference is. Is one to do with visuals and the other with content? Are they more or less interchangeable? Do they have different responsibilities? Can you have both in the same shop?
Is one to do with visuals and the other with content?
An article published "Creative Director vs. Art Director":
Are they more or less interchangeable?
Art Directors at bigger studios or corporations often oversee just a particular segment of design or at least different teams. So you might have an art director for interactive design and another for package design. The Creative Director would oversee all these.
Do they have different responsibilities?
Can you have both in the same shop?
It all depends were you are sometimes its really just names and titles and they can be interchangeable.
Usually an Art director will work or lead other creatives (illustrators, photographers, designers, writers) to execute a concept or idea. Creative Directors are typically the person that sets the vision, & strategy for a brand, campaign or line. If you have both in a (big) company I think a Creative director can boss around multiple art directors.
I wrote an article exactly on this subject, let me know what you think: http://www.joelesina.com/the-difference-between-graphic-designer-art-director-creative-director/