Open source licenses are licenses that comply with the Open Source Definition — in brief, they allow software to be freely used, modified, and shared. To be approved by the Open Source Initiative (also known as the OSI), a license must go through the Open Source Initiative's license review process.
The following OSI-approved licenses are popular, widely used, or have strong communities (as defined in the 2006 Proliferation Report):
Many other licenses are also OSI-approved, but fall into other categories, such as special-purpose licenses, superseded licenses, or retired licenses. Complete lists that include all approved licenses are available:
The OSI maintains a FAQ, which includes a lot of useful background on open source licensing, including:
For more information about open source licenses and in particular about the Open Source Initiative's approval process, see: