The ShareAlike ("SA") element is found in two of the six CC licenses: BY-SA and BY-NC-SA. The ShareAlike mechanism is included in the version 4.0 licenses as follows:
- if You Share Adapted Material You produce, the following conditions also apply.
- The Adapter’s License You apply must be a Creative Commons license with the same License Elements, this version or later, or a BY-NC-SA Compatible License.
- You must include the text of, or the URI or hyperlink to, the Adapter's License You apply. You may satisfy this condition in any reasonable manner based on the medium, means, and context in which You Share Adapted Material.
- You may not offer or impose any additional or different terms or conditions on, or apply any Effective Technological Measures to, Adapted Material that restrict exercise of the rights granted under the Adapter's License You apply. 
The ShareAlike licenses are known as "copyleft" licenses: they use copyright to ensure that the freedoms associated with a licensed work survive as the work is modified and adapted by others, and that those freedoms attach to adaptations of the work as well. The ShareAlike license has several intended effects:
- The original work always remains freely available to use and remix. Anyone who has access to the work may use it, even if they encounter the work in a modified form.
- Adaptations of the work are always freely available to use and remix. Anything made from the original work is just as free as the original work was, and you may use a remix as a starting point for your own works just as easily as starting from the original work.
- The ShareAlike licenses are designed to result in the creation of new works for the commons through their copyleft mechanism. Because new contributions to adaptations (when distributed) must be licensed under the same or a compatible license, people who wish to remix SA works also contribute back to the commons as a condition of using the SA work.
Creative Commons also has the ability to name other copyleft licenses as compatible with the ShareAlike licenses, as explained below. Licenses that CC names as compatible will also have these characteristics.
The ShareAlike condition applies only for works considered adaptations under copyright law, not simply in collections with other works (also referred to as mere aggregations). When a ShareAlike work is remixed and shared, any Adapted Material must be licensed compatibly—but not all reuse of SA works creates Adapted Material. Simply including an SA work unmodified alongside unrelated materials does not produce an adaptation.
Compatible licenses are limited to those explicitly named. Though many licenses may work similarly to the ShareAlike licenses, Adapted Material may only be created and distributed under those licenses explicitly named on CC’s Compatible Licenses page. CC undertakes a detailed and participatory review process before naming any license as compatible in order to ensure that the expectations of its licensing community are being upheld. Only licenses approved through this process are compatible; any others must be evaluated by CC and the community to ensure that fundamental incompatibilities do not exist. You may ask CC to review a license according to the process if you believe it should be compatible.
The ShareAlike term applies to licensed uses only, not uses by the rightsholder. As with all CC licenses, the SA licenses only restrict what a reuser may do under the license and not what the licensor (rightsholder) can do. Licensors that make their works available under an SA license are always free to share their works under other terms if they wish.
ShareAlike does not limit uses otherwise allowed by limitations and exceptions to copyright. Nothing in the SA licenses (or any CC license) controls or conditions uses covered by an exception or limitation to copyright or similar rights, or otherwise controls any activity for which no permission under such rights is required. For example, in many jurisdictions, a person does not have to ShareAlike if the work as adapted is being used for purposes of criticism or parody. Similarly, because posting a link to a work does not require permission under copyright, a user may include a link to SA-licensed material on a website whose content is All Rights Reserved. In such cases, the CC license never comes into play and the SA and other conditions may be disregarded.
Explanations of ShareAlike do not modify the CC license. Some licensors or website providers state expectations or interpretations about what SA means. Those explanations never form part of the CC license, even if included in terms of service or another resource designed to contractually bind reusers. CC strongly discourages the practice when such statements carve back (rather than expand) on reuses allowed by the SA definition. When those statements are intended to modify the CC license in a way that limits the permissions otherwise granted by the license, no CC trademarks may be associated with either the work or the terms under which it is offered. For more information about CC’s license modification policy, visit this page on modifying the CC licenses.
Unless other restrictions are present, the work may be used for any purpose, without the need to make distinctions about allowable types of uses. One reason to use an SA license is that it allows creators to permit a broad range of persons and entities to use the work, without needing to trust that they will respect your desire to keep the work in the commons. Many licensors are concerned that a reuser will exploit their CC-licensed work, getting the benefit of it without giving anything back to the community that created it. Under the ShareAlike licenses, a licensor may use the work for any purpose whatsoever, so long as the work and any resulting adaptations are available under the SA or a compatible license.
The ShareAlike condition only applies when a work is publicly shared. You are not obligated to share things you make from SA works--you may create remixes and adaptations that you do not publish. If you are using ShareAlike materials privately and not sharing them with others, you do not have to comply with the license conditions. For example, if you translate a ShareAlike work for internal use within your office, you do not have to license your translation under an SA or compatible license unless you plan to share it with others.
ShareAlike photo being used unmodified in a larger work. Unless the larger work would be considered an adaptation of it, using a ShareAlike photo as a separate element within it does not require original materials in the larger work to be ShareAlike or compatible. The larger work may be licensed under any terms.
Translation of a ShareAlike work. The translation is an adaptation of the original ShareAlike work, and must be licensed compatibly. The SA-licensed original work is inseparable from the translation; it must be distributed under SA terms, as must the translator’s contribution.
Material from a ShareAlike-licensed course remixed to form another course. If an SA-licensed course (including, for example, material such as a textbook and lesson plan) is rearranged and remixed to form a differently-arranged course that is considered an adaptation of the original, the new course must be licensed compatibly with SA. (Note that non-SA materials may still be studied--for example, an SA-licensed course on photography may discuss non-SA photographs, but the instructional materials created for the course must be SA or compatible.) If the course *itself* is not under an SA license, but individual materials within the larger course are, then only if you reuse the SA-licensed content do you need to consider your obligations under the SA license.
ShareAlike material referenced in a course. You may refer to ShareAlike material in a course without affecting the licensing of the course itself. For example, any course on film studies may discuss an SA-licensed movie without requiring the course itself to be ShareAlike. This is because the course is not based on or derived from the SA film; the film is simply an item being studied.
ShareAlike music being used as the soundtrack to a video. This is one explicit requirement of the SA licenses, which provide that all synching of SA-licensed music with other content creates an adaptation. In these instances, the resulting video must be under a ShareAlike or compatible license.
Choosing SA for your content
Before opting to use an SA license for your material, consider the following:
- SA may be incompatible with other material you want to use in your remix. Because the ShareAlike licenses require that adapted material of a ShareAlike work be licensed under a ShareAlike or a compatible license, you should be aware of the licenses covering the other materials that you want to use in your remix.
- BY-SA allows your work to be used commercially. While the BY-SA license requires that commercial entities using the work comply with the terms of the license, they may sell or otherwise use your work or their adaptation of your work for commercial purposes.
- SA licenses may not be allowed by the institutions or publications you wish to create content for. (For example, some journals such as PLOS ONE require that all submissions be under the CC BY license.) You may offer other licenses for your work in this case, but the SA license alone will not be sufficient.
- Some potential reusers may not be willing or able to comply with the additional conditions of SA, which may limit reuse of your work.
- The operation of the ShareAlike license depends on what is an adaptation under a particular jurisdiction’s copyright law. As this may differ across jurisdictions, the effect of this license may also differ jurisdiction to jurisdiction.
- (Section 3(b) of the BY-SA 4.0 license)
- (What does create Adapted Material is not always easy to determine, and may differ across jurisdictions.)