: The article provides an overview of the legal relationships in Open Source Structures. It shows that – as within all software development and distribution models – different persons with different “functions” (developer, distributor, and user) can conclude contracts concerning various objects of agreement. 1 Legal Aspects of Open Source Software The terms “Open Source Software” or “Free Software” denote software that may be copied, distributed and modified by anyone, and the source code of which is at the same time freely available. Open Source Software thus establishes a structure of decentralised software engineering as well as decentralised software distribution. In contrast to “conventional” (“proprietary”) structures, the software is neither developed by individual corporations or organisations nor is it supplied exclusively by “authorised dealers”. Over the last fifteen years Open Source Software has gained considerable market shares in certain softw...