Copyright is a form of protection provided by Title 17, U.S. Code to the authors of original works, including literary, dramatic, musical, artistic, including material published in electronic format.
Copyright protection covers any work, published or unpublished.
Copyright protection subsists from the moment the work is created in fixed form, including digitally created works. The copyright in the work of authorship immediately becomes the property of the author who created the work.
You do not have to register your work with the U.S. Copyright Office for it to be protected by copyright.
Copyright law protects the expression of ideas or facts, not the ideas or facts themselves.
Copyright protection is not forever; see How long does copyright last? and the chart from Cornell about public domain material. See also the Google online books page maintained at UPenn for out-of-copyright works.
Works that have not been fixed in a tangible form of expression, such as choreographic works that have not been notated or recorded, improvisational speeches, or performances that have not been written or recorded.
Titles, names, short phrases, and slogans; familiar symbols or designs; mere variations of typographic ornamentation, lettering, or coloring; mere listings of ingredients or contents
Ideas, procedures, methods, systems, processes, concepts, principles, discoveries, or devices, as distinguished from a description, explanation, or illustration
Works consisting entirely of information that is common property and containing no original authorship, such as standard calendars, height and weight charts, tape measures and rulers, and lists or tables taken from public documents or other common sources).
Most of the information produced by the U.S. Government is not copyrighted and may be freely used. See U.S. Government Photos and Images; many are in the public domain.