Introduction to Apache License 2.0

Apache License 2.0 (commonly known as Apache 2.0 or ASL 2.0) is one of the most popular permissive open-source licenses. It was officially released in January 2004 by the Apache Software Foundation (ASF). As a classic permissive license, it allows almost unrestricted use, modification, and distribution of code — including incorporation into proprietary (closed-source) software — without the strong copyleft requirements found in licenses like the GPL.

Origin and Evolution

• 1995: Apache Group (predecessor of ASF) created the original Apache License 1.0 for the Apache HTTP Server.
• 2000: Apache License 1.1 — minor improvements, mainly simplifying the advertising clause.
• 2004: Apache License 2.0 — major revision that introduced explicit patent grants and a patent termination clause in response to rising software patent litigation risks at the time (e.g., the SCO vs. IBM case).

The 2004 revision struck a perfect balance between open-source freedom and commercial practicality, making Apache 2.0 especially attractive to enterprises while protecting contributors and users from patent trolls.

As of 2025, Apache 2.0 remains the default and only license for all new Apache projects. No major new version has been released, though community discussions have emerged around future enhancements (e.g., blockchain-based contributor compensation and fair-code principles). The core text, however, remains stable and is still regarded as a “gold standard” among permissive licenses.

Core Features

• Broad Permissions
  You may freely use, copy, modify, merge, publish, distribute, sublicense, and/or sell the software — including in proprietary products.

• Explicit Patent Grant
  Contributors automatically grant all users a perpetual, worldwide, royalty-free patent license for their contributions. If a contributor (or anyone) sues you for patent infringement over the licensed code, their patent license to you is automatically terminated (defensive termination clause).

• Notice & Attribution Requirements
  You must retain the original copyright notice, license text, and disclaimer in all distributions (including binary forms).

• No Copyleft
  Unlike GPL, derivative works do not need to be open-sourced. You can keep your modifications proprietary.

• As-Is Disclaimer
  The software is provided “AS IS” without warranties of any kind.

• License Compatibility
  Compatible with GPLv3 (but not GPLv2), making it easy to combine with many other open-source components.

Comparison with Other Popular Licenses

Feature	Apache 2.0	MIT	GPL v3 (Copyleft)
Permissive?	Yes	Yes	No
Length & Readability	Medium (~2 pages)	Very short (a few lines)	Long
Patent Grant	Explicit + defensive termination	None	Explicit (but weaker protection)
Can be used in proprietary software?	Yes	Yes	No (must remain open-source)
Commercial friendliness	Extremely high	Extremely high	Low
Typical users	Google, Microsoft, Apple, Android, TensorFlow, Kubernetes, Hadoop	Most small projects & libraries	Linux kernel, GNU tools

Popularity (2025): According to GitHub Octoverse and Open Source Initiative reports, Apache 2.0 remains the second most-used license worldwide (just behind MIT) and the #1 permissive license in enterprise and cloud-native projects.

Famous Projects Using Apache 2.0

• Android Open Source Project (AOSP)
• Kubernetes
• Apache Hadoop, Spark, Kafka
• TensorFlow
• Flutter (Google)
• Swift (Apple’s open-source parts)

In short, if you want maximum freedom, strong patent protection, and enterprise-friendly terms, Apache License 2.0 is still one of the best choices in the open-source world.