A software license defines the permissions, restrictions, and obligations that govern how software can be distributed, modified, and used. It acts as a legal framework that determines whether others can freely share, alter, or commercialize the code. For example, open-source licenses like the MIT License allow anyone to redistribute the software with minimal conditions, while proprietary licenses restrict redistribution to authorized parties only. Without a license, software defaults to exclusive copyright protection, meaning others cannot legally copy or distribute it. Licenses also clarify how derivative works (e.g., modified versions) must be handled, ensuring compliance with the original creator’s intent.
The choice of license directly impacts how developers can integrate and share software. Permissive licenses (e.g., Apache 2.0) enable broad usage, even in proprietary projects, as long as attribution is provided. In contrast, copyleft licenses (e.g., GPL) require derivative works to adopt the same license, ensuring modifications remain open-source. For instance, using a GPL-licensed library in an app often forces the entire project to become GPL-licensed, which may conflict with commercial goals. Developers must also consider dependencies: combining code under incompatible licenses (e.g., GPL and proprietary) can create legal risks. Tools like license-checkers help identify conflicts early, avoiding costly rework or litigation.
From a business perspective, licenses shape revenue models and community engagement. Open-source projects often rely on permissive or copyleft licenses to encourage collaboration, as seen with Linux (GPL) or React (MIT before its 2023 controversy). Proprietary licenses, however, protect monetization by restricting access to source code. Some companies use dual licensing (e.g., MySQL under GPL or a paid commercial license) to serve both communities and enterprises. Licensing decisions also affect contributor agreements: projects like Kubernetes require contributors to sign a CLA (Contributor License Agreement) to maintain legal control. Choosing the right license balances transparency, compliance, and sustainability for both developers and organizations.