Let’s begin with a little background. To modify software (e.g. to fix a bug or create a new functionality) you need its source code. Most commercial software is closed source, which means that only the company who made the software can change the software code. Open source software, on the other hand, can usually be accessed, used, changed, and shared without restriction. It’s typically made by many people, and distributed under open source licenses such as GPLv3 or BSD3.

Some open source licenses can be a gift and a curse. For example, the GPLv3 license requires licensees who share their programs with the world to submit the source code of modified and extended versions of a software program back to the open source community. So if you mix open source software and your own closed source software, you need to check whether the source code for the combined software product must be shared with the entire open source community – including your competitors.

It depends on what you want to achieve. For example, if you’re working with other companies on a solution that might become an industry standard, it’s important to prevent other companies modifying the program and making it ‘closed’ again. To make sure your solution – and any modified or extended versions – stay open source, you can use a “copyleft” license like GPLv3 or AGPLv3.