|This article relies on references to primary sources. (July 2011)|
Shared Source is an umbrella term covering some of Microsoft's legal mechanisms for software source code distribution. Microsoft's Shared Source Initiative, launched in May 2001, includes a spectrum of technologies and licenses. Most of its source code offerings are available for download after eligibility criteria are met.
The licenses associated with the offerings range from being closed-source, allowing only viewing of the code for reference, to allowing it to be modified and redistributed for both commercial and non-commercial purposes.
Shared Source programs allow individuals and organizations to access Microsoft's source code for reference (e.g. when developing complementary systems), for review and auditing from a security perspective (mostly wanted by some large corporations and governments), and for development (academic institutions, OEMs, individual developers).
As part of the framework, Microsoft released 5 licenses for general use. Two of them, Microsoft Public License and Microsoft Reciprocal License, have been approved by the Open Source Initiative as open source licenses and are regarded by the Free Software Foundation as free software licenses. Other Shared Source licenses are proprietary, and thus allow the copyright holder to retain tighter control over the use of their product.
Two specific Shared Source licenses are interpreted as free software and open source licenses by FSF and OSI. However, OSI president Michael Tiemann considers the phrase "Shared Source" itself to be a marketing term created by Microsoft. He argues that it is "an insurgent term that distracts and dilutes the Open Source message by using similar-sounding terms and offering similar-sounding promises".
 Restricted licenses
 Microsoft Reference Source License (Ms-RSL)
This is the most restrictive of the Microsoft Shared Source licenses. The source code is made available to view for reference purposes only, mainly to be able to view Microsoft classes source code while debugging. Developers may not distribute or modify the code for commercial or non-commercial purposes. The license has previously been abbreviated Ms-RL, but Ms-RL now refers to the Microsoft Reciprocal License.
 Microsoft Limited Public License (Ms-LPL)
This is a version of the Microsoft Public License in which rights are only granted to developers of Microsoft Windows-based software. This license is not open source, as defined by the OSI, because the restriction limiting use of the software to Windows violates the stipulation that open-source licenses must be technology-neutral. It is also considered to be non-free by the Free Software Foundation due to this restriction.
 Microsoft Limited Reciprocal License (Ms-LRL)
This is a version of the Microsoft Reciprocal License in which rights are only granted when developing software for a Microsoft Windows platform. Like the Ms-LPL, this license is not open source because it is not technology-neutral due to its restriction that licensed software must be used on Windows, and is also not considered free by the Free Software Foundation due to this restriction.
 Non-free licenses
- Microsoft Enterprise Source Licensing Program
Microsoft gives enterprise customers viewing access to some parts of some versions of the Microsoft Windows operating systems. The ESLP license agreement is among the most restrictive of the licenses associated with Shared Source programs, allowing no modifications of the code.
- Microsoft Windows Academic Program
The Windows Academic Program provides universities worldwide with concepts, Windows kernel source code, and projects useful for integrating core Windows kernel technologies into teaching and research.
- Microsoft Government Security Program
The Microsoft Government Security Program is an effort to assist national governments in evaluating the security of Windows and of other Microsoft products. Participating governments have access to the source code for current versions of Windows and Windows service packs, Windows Embedded CE, and Microsoft Office.
- Most Valuable Professionals Source Licensing Program
Through this program, Microsoft makes Windows source code available to members of their "Most Valuable Professional" program. MVPs are members of the developer and support community who have made significant public, volunteer contributions, primarily through participation in online forums. The MVP Source Licensing Program allows licensees to use the source code for debugging and support purposes, though it may not be used to aid in the development of a commercial product.
- Microsoft Shared Source Common Language Infrastructure
The first widely-distributed Shared Source program was Shared Source CLI, the Shared Source implementation of the Common Language Infrastructure. The licensing permits non-commercial modification and distribution of the source code, as long as all distributions include the original license, or one encompassing the original terms.
 Free licenses
- ASP.Net AJAX Control Toolkit
The ASP.NET AJAX Control Toolkit is a set of controls and extenders that use AJAX technologies to enable developers to improve the client experience on their web sites. The toolkit is licensed under the Microsoft Public license (MS-PL) and is available on CodePlex, Microsoft’s online community development portal for collaborative software development projects.
 See also
- Geekzone: Microsoft announces expansion of Shared Source Initiative
- "Open vs. Closed Source Software". scienceinafrica.co.za. January 2004.
- "ZDNet Definition for: Closed Source". ZDNet. "Proprietary software owned by one organization. The term is typically used only in discussions that contrast open source software with proprietary software"
- "Licenses - Free Software Foundation".
- RISC OS Open
- "Shared Source Common Language Infrastructure License".
- Microsoft Windows Embedded CE 6.0 Shared Source License Terms (“License”)
- Michael Tiemann (2007-11-11). "Who Is Behind "Shared Source" Misinformation Campaign?". Retrieved 2011-03-12. "Shared source is a marketing term created and controlled by Microsoft. Shared source is not open source by another name. Shared source is an insurgent term that distracts and dilutes the Open Source message by using similar-sounding terms and offering similar-sounding promises. And to date, 'shared source' has been a marketing dud as far as Open Source is concerned."
- "Microsoft Reference Source License". Microsoft. 2008-02-01. Retrieved 2008-02-13. ""Reference use" means use of the software within your company as a reference, in read only form, for the sole purposes of debugging your products, maintaining your products, or enhancing the interoperability of your products with the software, and specifically excludes the right to distribute the software outside of your company."
- "Microsoft Reference Source License".
- "Microsoft Reciprocal License (Ms-RL)".
- "Microsoft Limited Public License (Ms-LPL)".
- "The Open Source Definition". Open Source Initiative.
- "Microsoft Limited Reciprocal License (Ms-LRL)".
- "Government Security Program". Microsoft Corporation. Retrieved 2011-02-20.
- "Most Valuable Professionals Source Licensing Program". Microsoft Corporation. Retrieved 2011-02-20.
- As written in the license, examples of commercial purposes would be running business operations, licensing, leasing, or selling the Software, or distributing the Software for use with commercial products