From Practical Guidance when submitting journal articles: Understanding your rights (excerpt reproduced courtesy SPARC):
"Relationships are changing due to the rise of digital publishing in academia. In order to maximize the value of the research you produce in this new environment, it is important for you to take an active role in managing the copyrights to your work.
U.S. Copyright law gives the author of an original work, such as a scholarly article, the exclusive rights to reproduce, distribute, adapt, publicly perform, and publicly display the copyrighted work. Copyright protection is now automatic. The author obtains these exclusive rights at the moment the copyrighted work has been “fixed in a tangible medium,” such as when a written work has been saved on a computer’s hard drive or printed.
The author retains these exclusive rights up until the moment the author signs a written agreement to transfer some or all of these exclusive rights. (By contrast, an author may give others non-exclusive permission to use the copyrighted work in a variety of ways, including through verbal agreement.) A transfer of any exclusive right is truly exclusive—once transferred the author may no longer exercise that right. If the author intends to retain the right to make any further uses of the copyrighted work, or intends to grant others permission to make any use of the copyrighted work, the author must make this clear in a written transfer agreement.
As a scholar or scientist, when you publish in a journal you are typically asked by the publisher to sign such a transfer agreement, or contract, that describes the assignment of various rights to the publisher in the intellectual property you have created. Thus, the agreements often deprive you of certain rights that you may not wish to forfeit, such as your right to post your article on the public Internet or to make copies for classroom use. To take advantage of the greater opportunity now available to communicate your research results, you need these rights to the articles you produce."
The copyright holder has the exclusive right to copy, to prepare derivative works, to distribute, and to license the work. A traditional copyright license reserves all rights for the author; a Creative Commons license describes how the author allows the work to be used by others. For uses other than those explicitly licensed, or even for those uses permitted under law (such as fair use), researchers may contact authors for permission.