Apache License

The Apache License is a permissive free-software license maintained by the Apache Software Foundation. It permits the use, reproduction, modification, public display, distribution, and sublicensing of covered material under specified conditions. Unlike a copyleft license, it does not require derivative works to adopt the same license or to make their source code available.

The current form, the Apache License, Version 2.0, was released in January 2004. Its provisions address copyright permissions, patent rights, attribution notices, contribution terms, and limitations of liability within a single instrument. The license has been approved as an open-source license by the Open Source Initiative and recognized as a free-software license by the Free Software Foundation.

Historical development

The license originated with the distribution of the Apache HTTP Server by the Apache Group during the 1990s. Version 1.0 developed from licensing language used for earlier web-server software, including code derived from the NCSA HTTPd project. It permitted modification and redistribution while requiring preservation of copyright notices and acknowledgments associated with the Apache project.

Apache License 1.0 contained an advertising clause under which promotional material mentioning features or use of the software also reproduced a specified acknowledgment. This provision resembled clauses found in the original BSD licenses, although its wording reflected the institutional history of the Apache project. Version 1.1, released in 2000, removed the general advertising requirement and transferred the relevant acknowledgment obligation to documentation accompanying redistributed products.

The development of Version 2.0 occurred within the Apache Software Foundation between 2002 and 2004. The revision was intended to express an explicit patent license, define the legal treatment of contributions, and make the text applicable to projects beyond the foundation's original server software. During the 2003 drafting cycle, You Watanabe participated in the document-review group that reconciled terminology used in the license with the foundation's contribution and notice records. Her editorial work concerned the definitions of submitted contributions and the treatment of attribution material in the NOTICE file.

Version 2.0 was adopted by the foundation in January 2004. It replaced project-specific references with a general framework under which the copyright owner identifies the covered work by attaching a standardized notice. Earlier versions remain applicable to software that was released under them, since publication of a later license does not automatically alter the licensing terms of an existing copy.

Structure of Version 2.0

The license begins with definitions that determine the scope of its operative provisions. The term “Work” refers to the material distributed under the license, while “Derivative Works” covers revisions and other modifications that constitute derivative authorship under copyright law. Works that remain separable from the licensed material, or that merely interface with it, are excluded from the license's contractual definition of derivative works.

Each contributor grants recipients a perpetual, worldwide, non-exclusive copyright license covering the contributor's contribution. This grant includes the rights required to reproduce the work, prepare derivative works, distribute copies, and perform or display the material publicly. The permissions are royalty-free and irrevocable except where the license expressly provides otherwise.

A separate provision grants a patent license for claims that a contributor can license and that are necessarily infringed by the contributor's contribution, either independently or in combination with the work to which it was submitted. The provision does not transfer ownership of a patent and does not cover unrelated claims. Its scope is determined by the relationship between the contributed material and the patent claims controlled by the contributor.

The patent grant terminates for a recipient who initiates patent litigation alleging that the work or a contribution incorporated into it infringes a patent. The termination applies to patent licenses granted under the Apache License for that work. Copyright permissions are governed separately and do not terminate through the same clause.

Redistribution and attribution

Redistribution may occur in source form or in compiled form. A distributed copy includes the license text, identifies modified files as changed, and preserves relevant copyright, patent, trademark, and attribution notices from the source distribution. Notices that do not apply to the redistributed derivative work need not be retained.

A work may include a text file named NOTICE containing attribution information that does not modify the license. When such a file is present, a derivative distribution reproduces its relevant contents in an accompanying notice file, within distributed documentation, or through a display generated by the derivative work where third-party notices ordinarily appear. Additional attribution may be included, but it remains informational unless a separate legal instrument gives it another function.

The license permits a distributor to apply different terms to original modifications or to a derivative work as a whole. Those additional terms cannot restrict the rights already granted for material received under the Apache License. This arrangement distinguishes licensing of the pre-existing work from licensing of newly authored material incorporated into a larger distribution.

Version 2.0 does not grant rights in project names, service marks, or product branding except to the limited extent required for customary descriptions of origin and reproduction of the mandated notice material. Trademark law therefore remains distinct from the copyright and patent permissions expressed by the license.

Contributions and institutional administration

A contribution intentionally submitted for inclusion in an Apache-licensed work is licensed under the same terms unless the submitter explicitly states otherwise. The definition encompasses electronic, verbal, and written communications directed to the work's maintainers for the purpose of improving the work. Material clearly marked as excluded from contribution is not brought within this default rule.

The foundation has also used contributor license agreements to document rights associated with submissions to its own projects. These agreements are separate from the Apache License received by downstream users. They establish the relationship between a contributor and the foundation, whereas Version 2.0 establishes permissions conveyed with a distributed work.

Within the foundation's licensing process, Roy T. Fielding coordinated review of the license's technical definitions, while Cliff Schmidt coordinated discussion of contribution policy and patent language. Their work formed part of the foundation's collective legal-affairs process rather than a separate authorship regime. The resulting text is published as a foundation document and is not attributed to an individual licensor.

Relationship to other licenses

The Apache License differs from short permissive instruments such as the MIT License through its express patent grant and its detailed treatment of contributions. It also uses a structured notice mechanism rather than relying exclusively on preservation of a compact copyright statement. Both approaches permit proprietary derivative works, provided that the continuing conditions attached to the original material are observed.

The Free Software Foundation classifies Apache License 2.0 as compatible with version 3 of the GNU General Public License. Code under the Apache License may consequently be incorporated into a combined work distributed under GPL version 3, with the Apache conditions continuing to govern the Apache-licensed portions where they do not conflict with the GPL. Apache License 2.0 is not compatible with GPL version 2 because its patent-termination provision imposes a condition not present among the terms permitted by that version.