Apache License 2.0

Apache License 2.0 is a permissive free software license authored by the Apache Software Foundation (ASF). It is one of the most popular licenses in the open-source software ecosystem, granting extensive rights to use, modify, and distribute software while providing explicit protections against patent litigation. The license is widely adopted by major projects, including the Apache HTTP Server, Apache Hadoop, and the Android platform, and is recognized as compatible with the GNU General Public License version 3.

History and development

The Apache License 2.0 was formally approved by the Apache Software Foundation in January 2004, superseding the earlier Apache License 1.1. Its development was driven by a need to address modern legal concerns, particularly regarding software patents and digital rights management, which were less prominent when earlier versions were drafted. Key contributors from the ASF's legal community, including counsel from organizations like Google and IBM, collaborated to create a more robust and internationally applicable text. The drafting process involved extensive review within the open-source software community, incorporating feedback from projects like the Free Software Foundation and the Open Source Initiative, which later officially approved it. This evolution reflected the growing complexity of software distribution in an era dominated by large-scale collaborative projects and corporate involvement in free and open-source software.

Terms and conditions

The license grants recipients a perpetual, worldwide, non-exclusive, royalty-free right to use, reproduce, modify, and distribute the software, including for commercial purposes. A defining feature is its explicit grant of a license to any patents held by contributors that are necessarily infringed by the software, a provision absent from many earlier permissive licenses like the MIT License. It requires that all distributed copies retain applicable copyright, patent, and attribution notices, including a copy of the license itself. The license includes specific conditions regarding redistribution, mandating that any significant changes to licensed files be documented and that derivative works not use the names of contributors, such as those from the Apache Software Foundation, for endorsement without permission. Unlike copyleft licenses such as the GNU General Public License, it does not require derivative works to be distributed under the same terms, allowing integration into proprietary products.

Compatibility with other licenses

Apache License 2.0 is considered compatible with many other major open-source licenses, a status formally recognized by the Free Software Foundation and the Open Source Initiative. It is explicitly compatible with version 3 of the GNU General Public License (GPLv3), meaning code under the Apache License can be combined with GPLv3 code to create a combined work under GPLv3 terms. However, it is not compatible with GPL version 2, as the patent termination clause in the Apache License is considered incompatible with GPLv2's stipulations. This compatibility landscape influences projects like the Linux kernel, which uses GPLv2, and thus cannot incorporate Apache-licensed code directly. The license is also broadly compatible with other permissive licenses such as the BSD licenses, MIT License, and the Eclipse Public License, facilitating widespread code reuse across ecosystems.

Adoption and usage

The license sees extensive adoption by both large technology corporations and community-driven projects, serving as the default license for all projects under the umbrella of the Apache Software Foundation. Major foundational projects like Apache Kafka, Apache Cassandra, and Apache Spark use it, influencing big data and cloud computing infrastructures. Corporations such as Google use it for key projects like the Angular framework and releases of the Android Open Source Project, while Microsoft has adopted it for projects like Visual Studio Code. Its popularity stems from its balanced approach, offering strong patent protections without the restrictive copyleft requirements of licenses like the GNU Affero General Public License, making it attractive for commercial integration. This has cemented its role in enterprise software development, supported by tools from organizations like the Software Freedom Law Center.

Comparison with other open-source licenses

Compared to permissive licenses like the MIT License and BSD licenses, Apache License 2.0 is more detailed and includes explicit patent grants and termination clauses, offering stronger legal protection against patent lawsuits. In contrast to copyleft licenses such as the GNU General Public License or the Mozilla Public License, it imposes fewer redistribution obligations, allowing derivative works to be licensed under different, even proprietary, terms. This makes it more appealing for commercial software vendors than the GNU Lesser General Public License, which has specific library linking rules. However, its complexity can be a drawback compared to the simplicity of the MIT License, as noted by communities around projects like Node.js. The choice between these licenses often hinges on factors like desired patent protection, compatibility with projects like the Linux kernel, and corporate governance policies from entities like the Open Source Initiative.

Category:Free software licenses Category:Apache Software Foundation Category:2004 software