The Modified BSD License - An Overview

by Rowan Wilson on 10 November 2005 , last updated


The Berkeley Software Distribution License (BSD for short) is one of the most commonly used open source licences. Approximately seven percent of the open source-licensed projects on the software repository Sourceforge use some form of BSD licence. Although this may sound like a small proportion, it does in fact make it the third most popular open source licence (the GPL and LGPL are ahead of it and account for almost eighty percent of open source licensing). This document attempts to draw together the main features of the Berkeley Software Distribution License into a friendly and comprehensible digest, and in addition to note some details about its history and usage. The licence itself can be read at

History of the BSD License

The University of California at Berkeley has a long history of pioneering software development and software distribution models. Having existed in some form since the early 1980s, the BSD licence can claim to be the oldest of the open source licences. In fact its long life has resulted in there being more than one version, and it is slightly misleading to speak of the BSD licence as a result. Although the history of its evolution is an interesting one, for the purposes of this document we will confine ourselves to detailing the last major revision that resulted in what is today called the modified BSD licence or the new BSD licence.

Until the late 1990s, many instances of the BSD licence included the following clause:

All advertising materials mentioning features or use of this software must display the following acknowledgement: This product includes software developed by (developer).

As reasonable as this might seem, it threatened to make the practice of aggregating open source software extremely impractical. Someone who wanted to publish such a collection might include hundreds of pieces of software, all with an adapted version of that clause. The obvious result would be that any promotional materials would have to include line after line of acknowledgements, leaving almost no room for logos, images or details. As it became clear that this was becoming a real problem, the Free Software Foundation lobbied Berkeley’s legal department to reissue the licence without the advertising clause. This they did, creating the new BSD licence. Of course, there are still hundreds of pieces of software out there licensed under the old version, and effort continues to contact the authors and persuade them to reissue their work under the revised licence.

A note about the nomenclature of BSD licences: terms such as “modified BSD licence” are informal terms, rather than the name used on the licences themselves. The original BSD licence can be identified by the presence of 4 clauses. The “modified” version discussed here is also referred to by other terms such as “new”, and can be identified by its having only 3 clauses. Finally, a variation on the 3 clause “modified” licence was recently approved, containing only 2 clauses; this is referred to as the “simplified” BSD licence.

Main Features of the BSD License

Even before the removal of the advertising clause, the Berkeley Software Distribution License was refreshingly short. It fits easily onto one side of a sheet of paper, and is relatively free of verbiage. A licensee of BSD-licensed software can:

  • use, copy and distribute the unmodified source or binary forms of the licensed program
  • use, copy and distribute modified source or binary forms of the licensed program provided that:

  • all distributed copies are accompanied by the licence
  • the names of the previous contibutors are not used to promote any modified versions without their written consent

Other Features of the BSD License

When comparing the BSD licence to other open source licences such as the GPL or the MPL, it is clear that it does not try to exercise anywhere near as much control over its licensees. In consequence, a licensee can take some code that is licensed under the BSD licence and incorporate it into their closed source work. A licensee can take BSD-licensed code and add to it, safe in the knowledge that whatever they contribute can be distributed in whatever way they choose. For this reason the licence is seen as friendly to traditional software business models that depend upon keeping the source private and capitalising on the sale of licensed binaries. Code that enters a traditional software business as BSD-licensed need not be distributed that way, and thus competitive advantage in the traditional sense can be maintained.

Another result of the BSD licence’s simplicity and brevity is that code licensed under it can be distributed alongside code licensed under the GPL without problems. In general this kind of distribution is hampered by the fact that the GPL demands that no additional restrictions are placed on its licensees. In practice this means that no licence which features a restriction that is not in the GPL is compatible with the GPL. The new BSD licence’s only restriction - that the original authors’ names not be used in promotion without their permission - is present in the GPL. Therefore, the BSD licence is compatible with the GPL.

What Does the BSD Do?

These bullets are intended to summarise the salient points of the BSD licence. They are not intended as a full description of its features. The BSD licence

  • allows code licensed under it to be incorporated in closed source software
  • allows code licensed under it to be incorporated in GPL-licensed software

OSS Watch has produced a document that highlights the main legal issues to consider when Making your code available under an open source licence.

Further reading


Related information from OSS Watch: