Introduction

The PHP programming language has undergone a significant change in its licensing structure. After years of operating under its own PHP License alongside the Zend Engine License, the PHP project has officially retired its custom license and adopted the three-clause BSD license. This move simplifies compliance and aligns PHP with a widely recognized open-source standard. The announcement was made via a blog entry detailing the process and approvals required.

Background: The Original PHP Licensing

Since its inception, the PHP codebase has been distributed under a unique license created by the PHP Group. The PHP License is a permissive open-source license, but it includes specific terms regarding the use of the PHP name and logo. Additionally, parts of the core engine—originally developed by Zend Technologies—were covered by the Zend Engine License. This dual-licensing arrangement created complexity for downstream users and contributors, as they had to navigate two distinct legal frameworks.

Why Change Now?

The decision to retire the PHP license was driven by a desire for simplicity and interoperability. The BSD 3-Clause License is one of the most widely used permissive licenses in the open-source ecosystem. It allows redistribution and modification with minimal restrictions, requiring only attribution and a disclaimer of liability. By adopting this license, PHP reduces barriers for adoption and integration with other projects, especially those that already use BSD or similar licenses.

The Process: More Than an RFC

Transitioning to a new license was not a simple vote. According to the project’s announcement, the journey involved several key steps:

• Securing consent from original PHP Group members: The PHP License grants the PHP Group authority to amend the license, but each original member had to be tracked down and provide written approval. Every single member consented.
• Approval from Perforce Software: As the successor to Zend Technologies, Perforce held rights to the Zend Engine License. They issued a formal letter confirming their full authority and support for the relicensing.
• Legal review: An attorney was hired to review the proposal and advise on any legal questions that might arise during the discussion period.
• Community discussion: A six-month period was opened for community feedback before the final vote. The vote passed unanimously.

Detailed Timeline

The entire process took several months, as documented in LWN’s coverage in March. The project required consensus from all stakeholders, which was achieved through painstaking communication and legal due diligence.

Benefits of the BSD 3-Clause License

The switch to BSD brings several advantages to the PHP ecosystem:

1. Wider compatibility: BSD-licensed code can be freely combined with code under many other open-source licenses, including GPL, MIT, and Apache.
2. Reduced confusion: Developers no longer need to distinguish between the PHP License and Zend Engine License. A single, standard license governs all of PHP.
3. Simpler contributions: New contributors can rely on a well-known license, lowering the legal barrier to entry.
4. Corporate friendliness: Many companies have legal teams that are already familiar with BSD terms, making integration into proprietary products smoother.

Impact on the PHP Community

This relicensing applies to the entire PHP source code, including the core engine and all standard libraries. Existing projects that use PHP do not need to change their own licenses; the change only affects the PHP code itself. The PHP Group expects no disruption to end-users, as the new license is equally permissive. Open-source purists have praised the move as a step toward standardization.

What About the Zend Engine?

The Zend Engine, originally developed by Zend Technologies, has been a critical part of PHP since version 4. With Perforce Software’s approval, the engine is now also covered by the BSD license. This unification means that PHP is now entirely under one license, eliminating the historical dual-licensing issue.

Conclusion

The retirement of the PHP license marks the end of an era and the beginning of a simpler, more unified licensing framework. The careful process—involving original group members, Perforce Software, legal counsel, and the community—ensured that every stakeholder had a voice. PHP remains a permissive open-source project, now under a license that is even more widely recognized. For more details, read the original blog entry or the LWN article.