Open source software licences are based on two fundamental principles: the possibility for users to use the software for any purpose and the possibility to modify and redistribute it without prior authorisation from the initial developer. Some open source software licences, like the General Public Licence (GPL), also impose a corollary obligation on the licensee: to make the source code available to other developers. The idea behind this form of licensing is that when programmers can read, redistribute and modify the source code for a piece of software, the software evolves. A number of legal challenges need to be addressed in order to ensure the most efficient deployment of open contentlicences in Europe and in the Netherlands, not least because most open source licences originate from the United States. This study gives an overview of the current legal situation regarding the use of open source software licences and investigates how the most commonly used open source software licences measure up to Dutch and European law. How does the distinct production and distribution model of open source licences fit in the current legal framework? Does the current legal environment support the use of open source licences or does it rather impede their use? In this last case, would certain adaptations to the law or to the licence terms be appropriate? By its in-depth analysis and clear conclusions, Unravelling the Myth around Open Source Licences amply contributes to the understanding of this complex field that policy makers, regulators, and academics so crucially require. Taking the provisions of the GNU GPL, the BSD, and the Mozilla Public Licence as examples, it investigates the implications of open source licensing from a private law, copyright law and patent law perspective. It also takes a brief look at the issue of the enforcement of these licences. To facilitate the use and enforcement of open source software licences in Europe, and more particularly in the Netherlands, the authors conclude their study by making a number of recommendations for the adaptation of the licence terms with a view to enhancing their compliance with the legal requirements. Lucie Guibault is Senior Researcher at the University of Amsterdams Institute for Information Law (IViR). Ot van Daalen is an attorney with the firm of De Brauw Blackstone Westbroek in Amsterdam. This is Volume 8 in the Information Technology and Law (IT&Law) Series.