Copyright is a form of protection provided by the laws of the United States (title 17, U.S. Code) to the authors of “original works of authorship,” including literary, dramatic, musical, artistic, and certain other intellectual works. This protection is available to both published and unpublished works. The 1976 Copyright Act generally gives the owner of copyright the exclusive right to do and to authorize others to do the following:

• reproduce the work in copies or recordings
• prepare derivative works based upon the work
• distribute copies or phonorecords of the work to the public by sale or other transfer of ownership, or by rental, lease, or lending
• perform the work publicly, in the case of literary, musical, dramatic, and choreographic works, pantomimes, and motion pictures and other audio­ visual works
• display the work publicly, in the case of literary, musical, dramatic, and choreographic works, pantomimes, and pictorial, graphic, or sculptural works, including the individual images of a motion picture or other audiovisual work
• perform the work publicly (in the case of sound recordings*) by means of a digital audio transmission

In addition, certain authors of works of visual art have the rights of attribu­ tion and integrity as described in section 106A of the 1976 Copyright Act. For further information, see Circular 40, Copyright Registration for Works of the Visual Arts.

It is illegal for anyone to violate any of the rights provided by the copyright law to the owner of copyright. These rights, however, are not unlimited in scope. One major limitation is the doctrine of “fair use” (section 107 of the 1976 Copyright Act). See the "Fair Use" tab above for more information.

(Extracted from "Copyright Basics", United States Copyright Office, used under 17 USC § 105)

What does copyright protect? Copyright, a form of intellectual property law, protects original works of authorship including literary, dramatic, musical, and artistic works, such as poetry, novels, movies, songs, computer software, and architecture. Copyright does not protect facts, ideas, systems, or methods of operation, although it may protect the way these things are expressed. 

What does public domain mean?  "Public domain" is the name given to a work that is not protected by copyright, patent, trademark, trade secrets, or contract laws or regulations.

What materials are in the Public Domain? See Cornell University's Copyright Term and the Public Domain in the United States 

How is a copyright different from a patent or a trademark? Copyright protects original works of authorship, while a patent protects inventions or discoveries. Ideas and discoveries are not protected by the copyright law, although the way in which they are expressed may be. A trademark protects words, phrases, symbols, or designs identifying the source of the goods or services of one party and distinguishing them from those of others.

When is my work protected? Your work is under copyright protection the moment it is created and fixed in a tangible form that it is perceptible either directly or with the aid of a machine or device.

Do I have to register with the Copyright Office to be protected? No. In general, registration is voluntary. Copyright exists from the moment the work is created. You will have to register, however, if you wish to bring a lawsuit for infringement of a U.S. work. 

Why should I register my work if copyright protection is automatic? Registration is recommended by the Copyright Office for a number of reasons. Many choose to register their works because they wish to have the facts of their copyright on the public record and have a certificate of registration. Registered works may be eligible for statutory damages and attorney's fees in successful litigation. Finally, if registration occurs within 5 years of publication, it is considered prima facie evidence in a court of law. 

Is my copyright good in other countries? The United States has copyright relations with most countries throughout the world, and as a result of these agreements, we honor each other's citizens' copyrights. However, the United States does not have such copyright relationships with every country. For a listing of countries and the nature of their copyright relations with the United States, see Circular 38a, International Copyright Relations of the United States.

(Some content from "Copyright in General", United States Copyright Office, used under 17 USC § 105)