The Open Source Definition

This section contains the full text of the Open Source Definition we described earlier in this chapter. You will find the text, with any updates, at:

On the Web, you may encounter other examples of “open source” licenses, particularly in situations where corporations are distributing the source code for their applications (while still retaining strict proprietary control over it). You will generally recognize these situations because at some point you’ll be asked to accept some kind of disclaimer before they allow you to continue a download. Just remember that the definition found at is the one “true” definition with which any other license provisions must comply. Accept no substitute—especially if you’re thinking of helping to develop an open source project of your own.

Here is the text of the Open Source Definition, in italics, with an explanation following each section:

  1. Free Redistribution

    The license may not restrict any party from selling or giving away the software as a component of an aggregate software distribution containing programs from several different sources. The license may not require a royalty or other fee for such sale.

    You can make as many copies of a program as you like to keep, sell, or give away. You don’t have to pay anyone for this privilege.

  2. Source Code

    The program must include source code, and must allow distribution in source code as well as compiled form. Where some form of a product is not distributed with source code, there must be a well-publicized means of obtaining the source code for no more than a reasonable reproduction cost—preferably, downloading via the Internet without charge. The source code must be the preferred form in which a programmer would modify the program. Deliberately obfuscated source code is not allowed. Intermediate forms such as the output of a preprocessor or translator are not allowed.

    The source code must be available for you to to test, fix, and explore program code. This is the fundamental tenet of open source, the open source equivalent of “thou shalt not kill.” Clever tricks, such as deliberately making the source code unreadable or providing intermediate forms of code (such as the C code output from original Pro*C programs) violate this provision.

  3. Derived Works

    The license must allow modifications and derived works, and must allow them to be distributed under the same terms as the license of the original software.

    You are allowed to change the original program in any way you wish (for example, in order to fix bugs or, in your opinion, improve the program). If you wish, you can then redistribute it under the same license as the original; alternatively, you may be allowed to choose another licensing type for derived works.

  4. Integrity of the Author’s Source Code

    The license may restrict source-code from being distributed in modified form only if the license allows the distribution of “patch files” with the source code for the purpose of modifying the program at build time. The license must explicitly permit distribution of software built from modified source code. The license may require derived works to carry a different name or version number from the original software.

    In order to protect the original program authors, an open source license may restrict the distribution of modified source code if it also allows you to distribute patch files to modify it indirectly. Consider an example from the everyday world. You may receive a book written by a friend, but you aren’t allowed to scribble in it before handing it on to a third acquaintance; however, you are allowed to make copious notes and, instead, distribute them in a separate notebook, clearly indicating that you are the second author. The original author also has the right to keep the original name. If you create derived works, you may have to rename your product. Similarly, you cannot change the cover title of your friend’s book, but under this model, you can copy the entire book word for word, add a few chapters (which you presumably think improves the book), and then republish it under another name.

  5. No Discrimination Against Persons or Groups

    The license must not discriminate against any person or group of persons.

    The license cannot stipulate who can and cannot download the program. For instance, the license cannot say, “Everyone can download this program except Englishmen with Scottish-sounding names, or Americans with Irish-sounding ones.” Fortunately for those of us suffering from such a condition, open source plays no favorites.

  6. No Discrimination Against Field of Endeavor

    The license must not restrict anyone from making use of the program in a specific field of endeavor. For example, it may not restrict the program from being used in a business, or from being used for genetic research.

    This clause builds on the previous clause by stating that the license may not stipulate what you can or cannot do with the downloaded program—for example, “My program cannot be used to promote Anglo-American authorship collaboration.” (This point has raised much debate within the open source community, but it has been concluded that potentially difficult political arguments should be left to courts and legislatures.)

  7. Distribution of License

    The rights attached to the program must apply to all to whom the program is redistributed without the need for execution of an additional license by those parties.

    The license must come fully and automatically into force when the program is downloaded, and must not require that any secondary licenses be obtained. For example, the license cannot state, “Now that you’ve downloaded this program, you must apply to for enhanced and specific permission to modify the program.”

  8. License Must Not Be Specific to a Product

    The rights attached to the program must not depend on the program’s being part of a particular software distribution. If the program is extracted from that distribution and used or distributed within the terms of the program’s license, all parties to whom the program is redistributed should have the same rights as those that are granted in conjunction with the original software distribution.

    The license cannot restrict your rights if you acquire it from other than the usual source. Therefore a license cannot say something like the following: “You only acquire full rights with this program if you download it within the software bundle designed by”

  9. License Must Not Contaminate Other Software

    The license must not place restrictions on other software that is distributed along with the licensed software. For example, the license must not insist that all other programs distributed on the same medium must be open-source software.

    The license may not say something like, “You are only allowed full rights to this program if you use it on a Linux platform.” You should be able to use the downloaded program with any other program combinations or on any platform you like, without losing any of the original rights.

For a shorter official description of the Open Source Definition, with a step-by-step rationale for each of the nine conditions, see:


The earliest versions of the Open Source Definition contained a tenth commandment, detailing the various acceptable license types (such as the Perl Artistic License). Like the black riders in The Lord of the Rings, however, the first nine steps of the definition were judged to be the important ones. The older conformance commentary was replaced by an objective certification program of marked and approved license types. For the latest details on this, check the following page:

Get Oracle and Open Source now with the O’Reilly learning platform.

O’Reilly members experience books, live events, courses curated by job role, and more from O’Reilly and nearly 200 top publishers.