Open Source software is software distributed under a license that complies with the Open Source Definition (OSD). In plain terms, Open Source software can be used, studied, modified, and shared by anyone without needing further approval from its original authors. Licenses are a legal tool to define and communicate what a user can, can’t, and must do to use a piece of software.
To be considered Open Source, software must meet the ten criteria set by the Open Source Initiative’s (OSI) Open Source Definition (OSD). These criteria include allowing free redistribution, providing source code, permitting derivative works, and not discriminating against any use cases (or fields of endeavor), among others. Any license that meets these criteria and is approved by the OSI is considered an “OSI Approved License®.” Well-known examples of licenses that meet the OSD include MIT, Apache 2.0, GPL, and BSD, all of which allow anyone to use, modify, and share the software for any purpose.
“Open Source” does not simply mean you have access to the source code. It also means you can legally use and reuse the code without asking the owner for permission. If code is made available without permissions to use and reuse it, it can be described as “source available” software. For software to be truly Open Source, it must grant perpetual permission to use, study, modify, and redistribute the code.
Open Source software can be used commercially. While non-commercial licenses exist, the Open Source Definition permits commercial use and redistribution, and many businesses build products and services on Open Source code. Organizations adopt Open Source software because it is cost-effective, adaptable, and supported by active communities. Commercial involvement can strengthen these projects through funding, testing, and long-term maintenance. Open Source doesn’t mean non-commercial—it means the license grants broad rights, including the freedom to use, study, modify, and share the software.
Free software vs. Open Source software
“Free software” is often used interchangeably with “Open Source.” Are they the same? In practice, yes – free software and Open Source software refer to the same set of freedoms. The terms are different because they stem from different philosophical approaches. The Free Software Foundation (FSF) prefers “free software” to highlight the importance of upholding the freedom to use, share and modify software. The Open Source Initiative uses “Open Source” to avoid confusing freedom with gratis, focusing on the benefits of open collaboration, sharing, use and modification of software.
There are different licenses that meet the OSI’s Open Source definition; each establishes things you must do, things you can do, and things you cannot do.
Collaboration to develop Open Source software
Open Source projects take many different forms, ranging from individual efforts that do not accept contributors to small dedicated teams within universities and nonprofit organizations, to large, distributed projects where volunteers from around the world collaborate with employees at technology companies.
Developing high-quality, maintainable, and well-documented Open Source software demands significant expertise and investment. Open Source principles go beyond guidelines for clear licensing—they are fundamentally about enabling collaboration. Open Source emphasizes the benefits of collaborative efforts between people who write code, draft documentation, report issues and bugs, implement features, and use the technology. Open Source is about sharing the benefits, as well as the burdens, by promoting the long-term sustainability, quality and maintenance of software projects.
Open Source also offers a pathway to make decisions about how projects develop over time, how decisions are made, who and how people contribute, what is prioritized, and what features are added and deprecated. In Open Source projects, project management and governance are affected by the processes, norms, and shared values of participants. Whether it’s a single maintainer, or code-producing nonprofits (e.g., foundations) coordinating thousands of volunteers, the decision-making process affects how Open Source projects evolve. Ultimately, Open Source sets the stage and provides a means for collaboration that benefits those who build the software and those who depend on it, ensuring that changes, improvements, and long-term maintenance are handled in a transparent and predictable way.
