MS-PL

"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.

Microsoft's Shared Source Initiative has been imitated by other companies such as RISC OS Open Ltd.

Microsoft also uses specific licenses for some of their products, for example the Shared Source CLI License and the Microsoft Windows Embedded CE 6.0 Shared Source License.

Two specific shared source licenses are interpreted as free software and open source licenses by FSF and OSI. However, former 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".

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