This article may be read in conjunction with 3 previous articles:
In these articles, I have discussed how someone comes to "own" a copyright in a work.
The default scenario is one in which the author of the work is the sole creator of the work. In that case, that person owns the copyright.
If an author works in conjunction with others, they all contribute copyrightable material and they all intend to create a joint work - those people may be "joint owners."
If an author creates a work for his or her boss and doing so is within the scope of employment OR if an author is commissioned to create a work, there is a signed agreement and the work falls within 1 of 9 categories - the work may be a "work made for hire" and the commissioning party owns the copyright.
This brings me to the final instance in which the owner of a copyright may be someone other than the person who created the work – copyright assignment.