Licensing
A license defines the rights and obligations that a licensor grants to a licensee. Open source licenses grant licensees the right to copy, modify and redistribute source code (or content). These licenses may also impose obligations (e.g., modifications to the code that are distributed must be made available in source code form, an author attribution must be placed in a program/ documentation using that open source).
Authors initially derive a right to grant a license to their work based on the legal theory that upon creation of a work the author owns the copyright in that work. What the author/licensor is granting when they grant a license to copy, modify and redistribute their work is the right to use the author’s copyrights. The author still retains ownership of those copyrights, the licensee simply is allowed to use those rights, as granted in the license, so long as they maintain the obligations of the license. The author does have the option to sell/assign, versus license, their exclusive right to the copyrights to their work; whereupon the new owner/assignee controls the copyrights. The ownership of the copyright (the "rights") is separate and distinct from the ownership of the work (the "thing") – a person can own a copy of a piece of code (or a copy of a book) without the rights to copy, modify or redistribute copies of it.
When an author contributes code to an open source project (e.g., Apache.org) they do so under an explicit license (e.g., the Apache Contributor License Agreement) or an implicit license (e.g., the open source license under which the project is already licensing code). Some open source projects do not take contributed code under a license, but actually require (joint) assignment of the author’s copyright in order to accept code contributions into the project (e.g., OpenOffice.org and its Joint Copyright Assignment agreement).
Placing code (or content) in the public domain is a way of waiving an author’s (or owner’s) copyrights in that work. No license is granted, and none is needed, to copy, modify or redistribute a work in the public domain.
Examples of free software license / open source licenses include Apache License, BSD license, GNU General Public License, GNU Lesser General Public License, MIT License, Eclipse Public License and Mozilla Public License.
The proliferation of open-source licenses is one of the few negative aspects of the open-source movement because it is often difficult to understand the legal implications of the differences between licenses.With more than 180,000 open source projects available and its more than 1400 unique licenses, the complexity of deciding how to manage open-source usage within "closed-source" commercial enterprises have dramatically increased. Some are home-grown while others are modeled after mainstream FOSS licenses such as Berkeley Software Distribution ("BSD"), Apache, MIT-style (Massachusetts Institute of Technology), or GNU General Public License ("GPL"). In view of this, open source practitioners are starting to use classification schemes in which FOSS licenses are grouped (typically based on the existence and obligations imposed by the copyleft provision; the strength of the copyleft provision).
An important legal milestone for the open source / free software movement was passed in 2008, when the US federal appeals court ruled that free software licences definitely do set legally binding conditions on the use of copyrighted work, and they are therefore enforceable under existing copyright law. As a result, if end-users do violate the licensing conditions, their license disappears, meaning they are infringing copyright.
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