Historically, copyright was for the greater good of the public, so there would be investment in the creation of written works and useful books for the public to purchase and learn from. It has evolved over the last 300 years into two primary aims. First, it has an utilitarian aim to incentivize creators to make a profit. Second, it recognizes author's rights so credit is given to the creators of original works. Copyright law is also specific to the country of origin, so it can vary from country to country.
Today, it's purpose is promoting the progress of science and useful arts, by securing for limited times to authors and Inventors the exclusive right to their respective writing and discoveries.
United States Constitution, Article I, Section 8
Full text of the Copyright Law in Title 17 of the United States Code.
Intellectual Property rights include copyrights, trademarks, and patents, all having limited durations. These protections exist independent of each other. For example, even though a work may be in the public domain due to expiration of copyright, it may have trademark or patent rights term protection still in effect.
Keep reading to learn more about items in the public domain and education exceptions which include fair use in the United States.
From Section 106 of U.S. Copyright Law, Copyright owners have the following exclusive rights to their work automatically and immediately after they are made in a fixed, tangible form:
See the Getting Permissions tab