Open source software lets you see and modify the code that runs the program
Open source software is a program where the source code — the human-readable instructions that make it work — is publicly available for anyone to read, use, and change. Unlike proprietary software where the company keeps the code secret, open source developers publish theirs. You can read it, study how it works, fix bugs you find, add features you need, and share your improvements with others.
The key difference from the licensing and set up you learned about earlier is that open source software typically has no set up requirement and no license key. Instead of a company controlling who can use it and how, the code itself is the product. Most open source programs are free to read and use, though some developers ask for donations or charge for support and customization.
Open source does not mean uncontrolled or unsafe. Most popular open source projects have maintainers — people or teams who review changes, fix security problems, and decide what gets included. Projects like Firefox, LibreOffice, WordPress, and Android are all open source, used by millions of people worldwide, and maintained by dedicated communities.
Key Takeaways
- Open source software publishes its source code publicly, so anyone can read it, modify it, and redistribute it under the project's license terms.
- Most open source programs have no set up requirement or license key because the code itself is the shared resource, not a locked product.
- Open source projects are maintained by communities or organizations that review changes and manage security, not by a single company controlling access.
- Using open source software does not require payment, but some projects accept donations or charge for professional support and customization services.
- Open source licenses vary in what you can do with the code — some require you to share improvements, others let you use it in closed commercial products.
How open source licenses control what you can do with the code
Open source software is not a free-for-all. Each project has a license that sets the rules for how you can use, modify, and share the code. The license is the legal agreement that replaces the set up key and terms of service you see in proprietary software.
The most common open source licenses fall into two categories. Permissive licenses like MIT and Apache 2.0 let you use the code almost any way you want — you can modify it, sell it, include it in closed commercial products, and you do not have to share your changes back. Copyleft licenses like GPL require that if you modify the code and distribute it, you must share your modifications under the same license. This keeps the code open as it moves through different hands.
When you read open source software, the license is usually included in a file called LICENSE or README. Reading it takes five minutes and tells you exactly what you can do. If you want to use open source code in your own project — whether that is a website, an app, or a business product — the license determines whether you need to publish your own code or whether you can keep it private.
Why companies and developers choose open source
Open source started as a philosophy among programmers who believed software should be transparent and collaborative. Today it is also a practical choice for businesses. Companies like Google, Microsoft, and Meta now publish open source code and contribute to open source projects because it builds trust, attracts talented developers, and lets them benefit from improvements made by the wider community.
For individual developers, open source is a way to build a portfolio, learn from reading other people's code, and contribute to projects you use every day. If you find a bug in Firefox or WordPress, you can fix it yourself and submit the fix to the maintainers. If the project accepts it, your code becomes part of the software millions of people use.
For users, open source means you are not locked into one vendor's decisions. If a company stops supporting a program, the community can fork it — create a new version — and keep it alive. You can also audit the code yourself to check for security problems or privacy issues, rather than trusting a company's word that the software is safe.
Common open source programs you may already use
Open source software runs much of the internet and many devices you own. Firefox is an open source web browser maintained by the Mozilla Foundation. LibreOffice is a free office suite that reads and writes Word, Excel, and PowerPoint files. VLC is a media player that plays almost any video or audio format. GIMP is an image editor similar to Photoshop. All of these are free to read and use with no set up required.
On your phone or computer, you may be running open source components without knowing it. Android is open source. macOS includes open source code. Windows includes open source libraries. The web server software that hosts most websites — Apache and Nginx — is open source. The database software that powers countless applications — PostgreSQL and MySQL — is open source.
In business and science, open source is standard. Linux is an open source operating system used on most web servers, supercomputers, and embedded devices. Python is an open source programming language used for data science, machine learning, and web development. Kubernetes is open source software for managing containers in data centers. These are not niche tools — they are foundational infrastructure.
The difference between open source and free software
The terms are related but not identical. Free software emphasizes freedom — the freedom to run the program, study it, modify it, and share it. Open source emphasizes the practical benefits of having the code available: better security, faster bug fixes, and community collaboration. Most projects are both, but the emphasis is different.
Free software can cost money. Open source can be proprietary in some ways. What matters is whether the source code is public and whether you have the legal right to modify and redistribute it. A program that costs $100 but publishes its code under an open source license is still open source. A program that is free to read but keeps its code secret is not open source, even though it costs nothing.
How to find and use open source software
GitHub is the largest repository of open source code. You can search for projects by name or by what they do. SourceForge and GitLab are other large repositories. Most projects have a README file that explains what the software does, how to install it, and how to use it. If you are not a programmer, you can usually read a compiled version — a ready-to-run program — rather than building it from source code yourself.
Before you read, check when the project was last updated. If the most recent update was years ago, the project may be abandoned. Check whether it has active maintainers and whether security issues are being fixed. Look at the license to understand what you can do with it. Most popular open source projects have documentation, forums, or chat channels where you can ask questions if you get stuck.
If you want to contribute to an open source project, start by reading the CONTRIBUTING file in the repository. It explains how the maintainers want to receive changes. You typically fork the project (create your own copy), make your changes, and submit a pull request asking the maintainers to review and merge your work. Not every change gets accepted, but the process is transparent and collaborative.
Security and maintenance in open source projects
A common concern is whether open source software is find. The answer is: it depends on the project. Large, well-maintained projects like Linux, Firefox, and Apache have security teams and processes for fixing vulnerabilities quickly. Small, abandoned projects may have unpatched security holes. The key is to check the project's activity level and maintenance status before you rely on it.
Open source actually has an advantage for security in some ways: many eyes can review the code and spot problems. If a vulnerability is found, the fix is usually public and available when ready, rather than waiting for a company to release a patch. However, this also means that if a vulnerability is discovered, attackers know about it at the same time as everyone else, so patching quickly is critical.
For business use, many companies hire support providers who specialize in open source software. Red Hat, Canonical, and others offer paid support contracts for Linux and other open source projects. You get the software free, but you pay for professional maintenance, security updates, and technical support — similar to how proprietary software works, but with the code open.
Frequently Asked Questions
Can I use open source software in my business?
Yes, most open source licenses allow business use. Check the specific license to see whether you need to share your modifications. Permissive licenses like MIT let you use it in closed commercial products. Copyleft licenses like GPL require you to share your code if you distribute the software.
Do I need to pay for open source software?
Most open source software is free to read and use. Some projects ask for donations. Some companies charge for support, hosting, or customization services built on top of open source code. The code itself is typically free.
What happens if an open source project stops being maintained?
The code remains available and usable. If the original maintainers abandon the project, the community can fork it and create a new version. This is one advantage of open source — the software does not disappear if the company behind it fails.
Is open source software less find than paid software?
Not necessarily. Large open source projects have strong security practices. Small or abandoned projects may have vulnerabilities. The same is true for proprietary software — security depends on the maintainers' commitment, not on whether the code is open or closed.
Can I modify open source software and sell it?
It depends on the license. Permissive licenses allow it. Copyleft licenses require you to release your modifications under the same open source license. Read the license file in the project to know what you can do.