The creator of an original work—whether it be a poem or a painting or a song—ordinarily has a copyright in that work under U.S. law. A copyright provides various exclusive rights over the work, conferred by the Copyright Act of 1976. Specifically, 17 U.S. Code § 106 gives the creator exclusive rights to reproduce, perform, and distribute the copyrighted work.
However, the creator of a copyrighted work does not always own the copyright. In some cases, other persons or entities own it—and the exclusive rights that go along with it. In other cases, multiple parties can share copyright ownership, if two or more people created the work. Finally, copyright owners can assign rights to the copyright to others, particularly for the purpose of marketing the protected work.
First, it's helpful to review the various exclusive rights granted to copyright holders by the Copyright Act of 1976:
This bundle of rights allows a copyright owner to be flexible when deciding how to realize commercial gain from the underlying work; the owner may keep those rights, or as outlined above, may sell, assign, or license any of the rights by contract.
As noted, there are exceptions to the rule that the creator of a work owns the copyright to the work. The most common exceptions involve some sort of employment relationship or contractual assignment from the creator to another person or entity, namely:
Work for employer: If an employee creates a work in the course of employment, the employer automatically owns the copyright to those works, absent any agreement to the contrary (such as language in an employment agreement). Imagine, for example, that Ana is a graphic designer for a large museum. She creates invitations for the museum's galas, posters for the museum's shows, and designs for its website. Even though Ana did all of this work herself using her own skills and creativity, those tasks were part of her job. The museum likely owns the copyright to all of Ana's designs—again, unless she has a contract saying otherwise.
Work made for hire: If an independent contractor creates a work that qualifies as a work "made for hire," then the hiring person or firm owns the copyright if the work is one of the following:
Works sold to another person or entity: Like many ownership interests, copyright is transferable. If the creator sells the entire copyright to another person or business, that buyer becomes the copyright owner. Copyrights can be bought and sold in the United States, just like other property rights (such as real property, personal property, or rights under a contract). There are many examples of this sort of "sale": a photographer can sell the copyright to a photograph to a magazine for a lump sum; a writer can ghost-write a novel for an author for a salary; or an artist can sell a design to a company for use as its website background.
When two or more authors prepare a work with the intent to combine contributions into inseparable or interdependent parts, the work is considered "joint work," and its authors are considered joint copyright owners. The most common example of a joint work is when a book or article has two or more authors.
The U.S. Copyright Office considers joint copyright owners to have an equal right to register and enforce the copyright. Unless the joint owners sign a written agreement to the contrary, each copyright owner has the right to commercially exploit the copyright, provided that the other copyright owners get an equal share of the proceeds.
When a copyright owner wishes to commercially exploit a work covered by copyright, the owner typically transfers one or more of these rights to the person or entity who will be responsible for getting the work to market, such as a book or software publisher.
When transferring copyright, it is common for a copyright owner to limit the rights being transferred. For example, the owner may restrict the transfer to a specific period of time, allow the right to be exercised only in a specific part of the country or world, or require that the right be exercised only through certain media, such as hardcover books, audiotapes, magazines, or computers.
When only some of the rights associated with the copyright are transferred, it is known as a "license." For more information on this, including exclusive licensing, see Should You License or Assign Your Art?
For a comprehensive guide to securing the use of copyrighted images, text, music, and more, see Getting Permission: Using and Licensing Protected Materials Online & Off, by Richard Stim.