自由／开源软件在一系列不同的许可下发布。有两种主要的许可类型，在其基础上衍生的许可则数不胜数。这两种基本的许可是 GNU （“GNU's not Unix”的迭代缩写）通用公共许可（General Public License, GPL）和 BSD 类许可。详细的许可列表可以在 FSF 的网站上找到：http://www.fsf.org/licenses/license-list.html。

=GNU 通用公共许可（GPL）=

这个许可的目的是永久保护用户的自由。用户几乎可以对 GPL 程序做任何他们想做的事，包括复制、分发和修改。许可的条件主要在软件传播给另一个用户时发生作用。

用 GPL 授权发布软件的主要要求是：

• GPL 程序的发布者必须对用户开放源代码。
• 发布者对 GPL 程序进行的任何改动也必须按 GPL 授权。
• 发布者不能对接受其 GPL 程序的用户提出任何非 GPL 的限制要求。
• GPL 软件的接受者享有与初始发布者同样的复制、修改和发布软件的权力。

GPL 软件占自由／开源软件的大多数，多达73％的自由／开源软件项目使用 GPL 授权[88]。在自由／开源软件中使用 GPL 的主要动力是一旦软件按 GPL 发布，它将永远具有 GPL 授权。任何人不能用附加的授权夺取用户重发布和修改程序的自由。商业软件公司因此不能在获取并修改 GPL 软件后将其在不同的私有软件授权下出售。

GPL 的全文可以在 http://www.fsf.org/licenses/gpl.html 找到。

=BSD 类许可=

BSD （Berkeley System Distribution，伯克利系统发布版本）类许可因为与加州大学伯克利分校最初的授权方式一脉相承而得名。这一类许可是最宽松的授权制度之一，因为它们允许用户在遵守以下条件的前提下对软件做任何事：

• 在源代码文件中包含最初的版权声明，从而承认最初授权人的著作权；
• 不因为其造成的损害起诉最初授权人或认定其应当负责。

早期的这类授权需要在所有宣传材料中提及加州大学伯克利分校（或任何发布原始软件的组织），但这一条款在最新版本中已经去掉了。

包括一些关键组件在内的大量的自由／开源软件项目都在 BSD 类许可下发布，例如：

• Apache 网页服务器－－当今因特网使用最多的网页服务器[89]
• XFree86 窗口系统－－自由／开源软件中几乎所有图形用户界面的基础
• FreeBSD, NetBSD 和 OpenBSD －－都是最初 BSD 版 Unix 的衍生版本；它们都在因特网上广泛应用，特别是 Yahoo 和微软 Hotmail 服务使用的 FreeBSD [90]。

BSD 类许可的代码很容易整合到商业应用软件中。过去就连微软也在 Windows 代码的网络部分使用了一些 BSD 的代码 [91]。许多公司把 Apache 网页服务器作为它们软件产品的一部分。与 GPL 不同的是 BSD 类许可不要求发布源代码，因此允许公司隐藏自己对初始代码的修改。公司也不用给用户查看、修改或发布被公司修改的部分代码的权力。

附录二是关于不同软件授权的更详细的列表。

FOSS is released under a variety of different licenses. There are two primary types of licenses and countless variants. The two main licenses are the GNU (recursive acronym for GNU’s not Unix) General Public License and the BSD-style licenses. A more detailed listing of licenses can be found on the FSF’s website at http://www.fsf.org/licenses/license-list.html.

The GNU General Public License (GPL)

This is designed to ensure that user freedoms under this license are protected in perpetuity. Users are allowed to do pretty much anything they want to a GPL program, including copying, distributing and modifying. The conditions of the license primarily affect the user when it is distributed to another user.

Among the key provisions of distributing GPL software are:
The distributor of a GPL program must also make available the source code to the recipient.
Any changes made to a GPL program by the distributor must also be licensed under the GPL.
Distributors may not place any non-GPL restrictions upon the users they distribute the GPL program to.
Recipients of GPL software are granted the same rights to copy, modify and distribute the software as the original distributor.

GPL software forms a significant majority of FOSS: as much as 73 percent of FOSS projectsi. One of the main motivations for the usage of the GPL in FOSS is assurance that once something is released as FOSS, it will remain so permanently. It is not possible to add additional licensing to strip away a user’s right to redistribute or modify the program. A commercial software company cannot take a GPL program, modify it and then sell it under a different, proprietary license.

The full text of the GPL can be found at http://www.fsf.org/licenses/gpl.html.

BSD-style Licenses

BSD-style (Berkeley System Distribution) licenses are so named because they are identical in spirit to the original license issued by the University of California, Berkeley. These are among the most permissive licenses possible, because they basically permit users to do anything they wish with the software as long as:
Attribution is given to the original licensor by including the original copyright notice in source code files; and No attempt is made to sue or hold the original licensor liable for damages.

Earlier versions required the acknowledgement of the University of California, Berkeley (or whichever organization released the original software) in all promotional material but this requirement has been dropped in most recent versions.

A large number of FOSS projects, including several critical components, are licensed under BSD-style licenses. Examples include:

The Apache Web Server – the #1 web server used on the Internet todayi
The XFree86 Window System - the foundation of almost all graphical user interfaces in FOSS systems
FreeBSD, NetBSD and OpenBSD – all variants based on the original Berkeley System Distribution (BSD) version of Unix; all are widely used on the Internet, especially FreeBSD, which runs Yahoo and Microsoft’s Hotmail servicesii

It is fairly easy to incorporate BSD-style licensed code into commercial applications. Even Microsoft has used some BSD code in the networking portions of its Windows codeiii in the past. Many companies include the Apache web server as part of their commercial software offerings. Unlike the GPL, BSD-style licenses do not require the distribution of source code, allowing a company to hide its modifications to the original code. Nor are companies required to grant users the right to view, modify or distribute the company’s modifications to the code.

A more detailed listing of different software licenses can be found in Annex II.