Free and Open Source Software (FOSS) is realised through legal instruments, private law agreements, licences, promises, and community norms. These private law instruments reside within a public law framework that grants exclusive and monopoly rights to creators of intellectual property. Written by FOSS experts, this work delivers an in-depth examination of the legal and commercial structures relating to the usage and exploitation of FOSS software. FOSS has become an increasingly important component of the ICT industry, embodied in the products that we use and the systems we depend on. Major industry players such as IBM have embraced FOSS and it impacts on all its users. This work will enable readers to understand the legal environment within which FOSS operates. The first part examines FOSS in relation to the key IP regimes. The commercial implications of FOSS are then examined from different components of the supply chain. The final part examines the implications of FOSS for policy makers.