Creative Commons is a non-profit organization created to realize the creative potential of the world-wide web by creating and supporting legal and technical tools for creators of web content. These tools allow creators to make their works readily available to others to reuse remix, etc. with attribution, while retaining other copy rights for themselves. The Creative Commons website, CreativeCommons.org, states their vision thus:
Their principal means of accomplishing this is by means of a suite of standardized licenses which can be easily understood and are searchable by web search engines, enabling anyone to easily find images, videos, music, etc, which are already cleared for reuse.
Until the Copyright Act of 1976, the US government required creators to register for copyright protection. If the new creation was not registered, it automatically entered the public domain. Since 1978 (when the Act took effect), a new creation falls under copyright protection automatically, as soon as it is fixed in a tangible form. Furthermore, this is true even if the author does not want or need to reserve these rights.
Additionally, the copyright term has been vastly expanded since the first copyright law was established in the U.S. Constitution. In 1790, copyright protection was in force for 14 years, with an additional one-time term extension of 14 years possible if the creator took steps to secure it. Since 1978, the maximum term is the life of the creator + 70 years for single-authored works, or up to 120 years after creation for other types of authorship. The effect of these changes is to vastly reduce the number of works entering the public domain. The chart below illustrates the trend.
)