Open-source licence
Also known as: open source license, open-source license, OSS licence, open source licence
An open-source licence is a legal licence that gives anyone permission to use, study, modify, and share software's source code, under certain conditions. 'Permissive' licences such as MIT and Apache 2.0 allow almost any use, including in commercial products. 'Copyleft' licences such as the GPL require that modified versions you distribute also be shared under the same licence.
While open-source licences make software freely available, ignoring their conditions can create real legal and business risks.
Open-source licence, explained at three levels
At home
An open-source licence is like the rules attached to a free community cookbook. You can use and change the recipes, but some cookbooks ask you to share your changes too.
At work
Licences decide whether a business can use open-source code in its products and what obligations come with it.
At home
Most open-source projects have a LICENSE file explaining the rules. MIT means you can do almost anything, as long as you keep the copyright notice.
At work
Permissive licences (MIT, Apache 2.0, BSD) have few conditions. Copyleft licences (GPL, AGPL) require sharing source code in some situations, with AGPL covering software offered over a network.
At home
'Free to download' doesn't always mean open source. In my opinion, checking the licence before building on someone's code is a good habit.
At work
Use software composition analysis tools to inventory licences, set approval policies for copyleft and source-available licences, track licence changes in dependencies, and involve legal counsel for distribution decisions.
Real-world examples
At home
Jerome wanted to use a free charting library in his side business. He checked that it used the MIT licence, which allowed commercial use.
At work
Nadia runs engineering at a Toronto software company preparing for acquisition. A licence scan found a GPL component that needed replacing before the deal closed.
How it compares
| feature | Permissive licence | Copyleft licence |
|---|---|---|
| Examples | MIT, Apache 2.0, BSD | GPL, AGPL |
| Use in closed products | Allowed | Restricted when distributed |
| Share changes | Not required | Required in many cases |
| Business risk | Low | Needs review |
Permissive licences ask little. Copyleft licences ask you to share alike.
For analysts
In vendor due diligence, I'd ask for a software bill of materials with licences. It surfaces legal risks long before they become expensive.
History & origin
Richard Stallman wrote the GNU General Public License (GPL) in 1989, using copyright law to keep software free, an idea called copyleft. Permissive licences such as the BSD and MIT licences grew out of universities in the 1980s. The Open Source Initiative, founded in 1998, created the Open Source Definition and approves licences that meet it. The Apache License 2.0 in 2004 added explicit patent protections. In the 2020s, companies including Elastic, HashiCorp, and Redis moved to 'source-available' licences restricting cloud providers, prompting community forks. In 2024, the Open Source Initiative published a definition for open-source AI, noting that many 'open' AI models don't qualify. In my view, licences are the quiet rules that hold the open-source world together.