What are the different types of open source licenses?

What is an open source license?

An open source license is a legal framework that governs how open source software can be used, modified, and distributed. Unlike proprietary software, open source software (OSS) allows users to access and modify the source code freely. However, this freedom comes with responsibilities, and each open source license defines the terms under which developers can use, share, and contribute to the codebase under its use.

What are the four main types of OSS licenses?

1. Permissive Licenses

Permissive licenses are characterized by their flexibility and are the most permissive of the four OSS license types. They allow for the modification and use of source code in proprietary projects without an obligation to share the derivative work. The Apache License 2.0, MIT License and the BSD License are popular examples of permissive licenses. 

2. Copyleft Licenses

Copyleft licenses, on the other hand, have a more stringent approach to code sharing. They require any derivative works to be distributed under the same license terms as the original software. This means that any improvements or modifications made to the software are to be made freely available to the community so that the open source nature of the project is maintained. 

Thus, copyleft licenses are not as good for developing a proprietary product or solution as permissive licenses due to the requirement to share any changes made to the source code. The General Public License (GPL) is a prominent example of a copyleft license.

3. Weak Copyleft Licenses

Weak copyleft licenses also require the full disclosure of changes made, but this requirement covers a narrower selection of code. Basically, only the source code from the original work (modified or not) must be made publicly available. Any additional code used does not. The Lesser General Public License (LGPL) is a well known example of a weak copyleft license. 

4. Public Domain Licenses

Public domain licenses take a unique approach by waiving all copyright and related rights, essentially placing the software in the public domain. Developers can freely use, modify, and distribute the code without any legal restrictions. While public domain licenses provide the most freedom, they also come with risks, as users may not have any legal protection or warranty. The Creative Commons Zero (CC0) license is an example of a public domain license. 

Graph describing the four different types of open source licenses

A quick history of the OSS license

While the exploration of the history of open source software and its various licenses is enough for an entire book, here are a few key milestones worth mentioning:

1985: Richard Stallman founded The Free Software Foundation (FSF), which played a crucial role in shaping the concept of free software. 

1989: The FSF introduced the GNU General Public License (GPL), which established the principle of copyleft. 

1992: The Linux kernel adopted the GPL.

1998: The Open Source Initiative (OSI) is established to promote and protect open source software. The OSI created the Open Source Definition, a set of principles that licenses must adhere to to be considered open source. The approval of licenses by the OSI provided a standardized way to categorize and understand the legal frameworks governing open source projects.

1999: The Apache HTTPd server is born, which would be the catalyst for the creation of The Apache Software Foundation and Apache License 2.0. 

2002: Mozilla launches FireFox under the Mozilla Public License.

Recent 2000’s: The permissive Apache License 2.0 has become the most widely used open source license since it strikes a balance between openness and commercial usability, making it an attractive choice for organizations seeking to contribute to and benefit from open source development.

Graph showing a brief history of the OSS license with seven important dates

OSS License spotlight: Apache License 2.0

One of the most widely used open source software licenses in the world is the Apache License 2.0. Distributed via The Apache Software Foundation, this license is a permissive open source license and as such allows users to freely use, modify, and distribute the software, even in proprietary projects, as long as the original copyright and license notice are included.

It promotes collaboration by offering a balanced approach that encourages open development while permitting commercial use. The Apache License 2.0 also includes an express grant of patent rights, and clear definitions for each term so that there’s much less room for ambiguity.

How to know if you need an open source license

The answer to this question is actually pretty straightforward: if you want your project to contribute to the open source ecosystem, then you will need to pick an open source license. This is because the license determines the terms that allow for the reproduction of any of the code used in the open source project.

If you don’t want your project to contribute to the open source ecosystem (in other words, if you aren’t okay with someone else modifying or using your code in one way or another), then you can skip out on the license completely. 

There are also resources online, like choosealicense.com, that can help you determine not only if you need an open source license, but also which one. 

How to choose an open source software license

While choosing an open source license doesn't have to be overly complicated, there are some key considerations to keep in mind when choosing an open source license for your software project, namely:

1. Project Goals

Understanding project goals is crucial when choosing a license, and that includes whether or not you’re comfortable with someone else distributing their own proprietary version of your project. For example, if you are okay with it, a permissive license could be a good choice. If not, a copyleft license may be more appropriate.

2. Commercial Use

Make sure you understand whether your chosen license permits commercial use of the software. Permissive licenses often allow for commercial exploitation, while copyleft licenses may impose restrictions on proprietary distribution.

3. Legal Counsel

When in doubt, seek legal advice. Open source licensing can be complex, and legal professionals can provide guidance to ensure compliance with licensing terms and regulations.

Graph with three tips for how to choose an OSS license


Open source licenses are the backbone of collaborative software development by providing the legal framework that governs how code is shared, modified, and distributed. The choice of an open source license significantly influences the dynamics of a project and impacts collaboration, adoption, and the degree of freedom granted to users and contributors.

Understanding the four main types of open source licenses enables developers and technology leaders to make informed decisions based on their project's goals and requirements. And by understanding the nuances of different licenses and their implications, developers can contribute to a thriving open source ecosystem while ensuring the success and sustainability of their projects.

DATE: Dec 15, 2023
AUTHOR: HotWax Systems
Enterprise Open Source Software, Open Source Software, apache